HEALTH POLICY AND PLANNING; 17(4): 402–411
© Oxford University Press 2002
Willingness to pay for treated mosquito nets in Surat, India:
the design and descriptive analysis of a household survey
MR BHATIA1 AND JA FOX-RUSHBY2
1Department of Social Policy, London School of Economics and Political Science, and 2Department of Public
Health and Policy, London School of Hygiene and Tropical Medicine, London, UK
For willingness to pay (WTP) studies to have an appropriate impact on policy making, it is essential that the
design and analysis are undertaken carefully. This paper aims to describe and justify the design of the survey
tool used to assess hypothetical WTP for treated mosquito nets (TMN) in rural Surat, India and report its
findings.
Results from qualitative work were used as an input for developing the WTP questionnaire. A total of 1200
households belonging to 80 villages in rural Surat were selected for the study. A bidding format was used
to elicit WTP values, using three different starting bids. The scenario was constructed in a way to reduce the
possibility of respondents acting strategically. The response rate was 100%. About 79% of the respondents
were willing to buy TMNs and the mean WTP was Rs57. Descriptive results of economic and other taste and
preference variables are also presented, which include preventive measures used by households and treatment seeking behaviour for malaria. It is observed that WTP as well as demographic variables and prevention methods differ significantly across arms of the trial.
This paper suggests that policy-makers could use the evidence following further analysis, along with information on costs of implementation, to ascertain the levels of subsidy that may be needed at different levels
of coverage.
Key words: willingness to pay, contingent valuation, demand, household survey, malaria, India
Introduction
As governments and international agencies think about the
balance between public and private provision and financing
of health care, they are becoming more interested in conducting, and considering the results of, studies about individual’s and household’s willingness to pay (WTP) for health
services. At the same time there is concern about the
reliability and validity of studies that focus on hypothetical
WTP (Johannesson 1993; Diener et al. 1998) as well as the
need to consider who is able to pay (Russell 1996). Given the
immediate policy relevance of WTP studies, it is particularly
important that the design and analysis is undertaken carefully.
This study was a part of the Malaria Control and Research
Project, which aimed to reduce malaria morbidity and
mortality by developing an effective and affordable malaria
control programme in Surat in order to contribute to development of a malaria control policy at national level. The overall
study set out to compare the effectiveness, efficiency and
acceptability of two malaria control interventions – in-house
residual spraying (IRS) and treated mosquito nets (TMNs) –
versus early diagnosis and prompt treatment (EDPT) in three
different ecological zones of Surat district over a 5-year
period via a triple-arm community randomized trial. To
evaluate the malaria control interventions, a community
randomized controlled trial was adopted, consisting of three
arms and covering a total of 126 villages of Surat district. The
interventions tested were in-house residual spraying by
deltamethrin and deltamethrin treated mosquito nets
(0.6 TMN per household member). The third arm (i.e.
control) was the case detection and treatment (Misra 1999).
Case detection and treatment was used as a baseline activity
carried out by dedicated project worker in each of the
126 villages throughout the trial. This part of the overall
study focuses on the general population’s WTP for TMNs as
questions have been raised both about whether the government should invest in this type of control strategy and the
extent of demand amongst potential consumers.
The paper aims to describe and justify the methods used in
designing a survey tool to assess hypothetical WTP for
treated mosquito nets in a rural area of Surat, Gujarat State,
India. It also outlines the study design and descriptive results,
and considers the implications of findings for survey design
and policy.
Methods
Theoretical framework and choice of variables
The neo-classical theory of demand is based on the assumption that individuals are capable of making rational choices
Willingness to pay for mosquito nets
between alternative goods to maximize their utility and that
this choice leads an individual to the point where their marginal value for a good equals the price paid. A demand curve
can be generated using the WTP values, and the area under
the demand curve used to estimate the social value of a good
or service. This research was based on the desire to measure
the consumer surplus attached to the purchase of TMNs, with
the expectation that this would lead to an increase in health
through a reduction in malaria. As the study was about the
purchase of new TMNs, it could be assumed that current
utility is held constant. Therefore, the focus was on using
compensating, rather than equivalent, variations (Johannesson and Jonsson 1991; Olsen 1997) and so questions concerning WTP were framed in terms of WTP for an increase of the
good.
It is important to know which variables affect stated WTP for
TMNs because this could help in assessing what factors may
encourage people to buy TMNs and at what price. Both have
potential policy relevance – it is important to know which
variables for example, would be under the control of policymakers other than just prices, so that the level of demand can
be influenced at all prices. As the main aim of economic
models of demand is to explain the quantity demanded of a
good in terms of economic variables, we needed to consider
the following: the price of the good as well as the price and
use of complements and substitutes for TMNs and income
and assets (e.g. ownership of land). In the case of TMNs, the
distinction between complements and substitutes is not
always clear. For example, other preventive measures like
mosquito coils could be considered substitutes but can be
used in conjunction with TMNs. We also outlined a range of
variables expected to represent and explain ‘tastes and
preferences’ in the following broad categories:
• personal characteristics of main earner and respondent
(e.g. age, gender, schooling, occupation);
• characteristics of household membership (e.g. size, number
of children, caste1);
• preferences for alternative methods of preventing
mosquitoes;
• knowledge of the cause(s) of malaria;
• treatment-seeking behaviour for malaria.
Development of the willingness to pay questionnaire
The role of qualitative methods in designing the household
survey
The aim of the qualitative research was to help develop the
survey questionnaire and to make the bridge from theoretical
models to relevant research questioning in Surat. For
example, whilst we knew which information about household
demand was needed, we had to determine how households
were variously defined and who would be the most appropriate respondent for considering purchasing a mosquito net.
Another example was the need to select an appropriate elicitation mechanism2 for use in Surat (we selected the bidding
format) as well as judging a suitable range of values for the
offer bids (we selected Rs50, Rs75 and Rs100 as starting bids
and 25, 100, 150, 200 as additional follow-up bids) such that
403
minimal ‘yes’ responses would be expected for the top value
in order to allow a demand curve to be estimated from bid
values alone. We also wanted to ascertain the range of potential response options for specific questions such as occupation
and sources of income. Finally, it was also designed to help
with practical issues such as the time when most respondents
would be available and the likely acceptability of the questions (e.g. whether people were likely to be willing to pay,
appropriate local language to use for malaria and willingness
to pay).
The qualitative methods used were semi-structured interviews and focus group discussions. Semi-structured interviews were held in all three ecological zones with: key
informants (n = 22) such as the Sarpanch (village head), community leaders and anthropologists working in the communities, who were asked about the community (e.g. ways to
define a household or to ask about income); mosquito net
owners (n = 21) and sellers (n = 20), who were asked for
details of prices and types of nets bought/sold and their
approaches to agreeing prices; shopkeepers (n = 17) and
pharmacists (n = 15), who were questioned on affordability,
credit systems and bargaining approaches used; and general
practitioners (n = 22), who were consulted on payments for
treatment. A team of two people, one to interview and the
other to take notes, conducted these interviews.
Twenty-five focus group discussions were conducted in 10
villages representing the three ecological zones. About six to
eight participants were selected on the basis of factors such as
age, sex, caste, occupation, religion and age of the last child.
The focus group discussion guides were prepared in advance
to gather information about: who is the head of the household; how purchase decisions are taken at the household
level; views on mosquito nuisance; the mosquito–malaria
link; preventive measures commonly used; treatment
seeking; expenditure on prevention and treatment of malaria;
satisfaction with government health facilities; need to buy
treated mosquito nets by time of year; appropriate mechanisms for delivery of treated mosquito nets; preferred modes
of payment; availability of cash; and the price for untreated
mosquito nets. The focus group discussions were conducted
according to the recommended format involving a trained
moderator and an assistant for taking notes. All were held in
Gujarati and lasted between 45 and 60 minutes.
WTP questions and the scenario for valuation
At the heart of any WTP study is the scenario for which
respondents are asked to give a value. Box 1 gives the English
translation of the scenario used. As questions about hypothetical WTP are prone to ‘strategic’ bias where respondents
over/under-estimate their ‘true’ personal values to effect a
specific outcome (Mitchell and Carson 1993), we attempted
to reduce such strategizing through the introduction of the
scenario – hence a balance between whether they or the
Government would have to pay.
The scenario for valuation needed to give all the relevant
information without overloading the respondent with
information, which is a difficult balance to achieve. The
404
Box 1.
MR Bhatia and JA Fox-Rushby
Introduction to, and description of, the scenario all respondents were asked to give their willingness to pay for
Introduction to the scenario
The National Malaria Eradication Programme (NMEP),a Government of India (GOI), is currently looking to decide how best to
control malaria. It is considering a number of options, one of which is dipping mosquito nets in insecticide. Unfortunately, this is quite
expensive for the GOI and so they want to know how much people are prepared to pay, in order to judge whether this intervention
will work in the future. Your responses to this section would be used for such a policy decision. You may be required to pay according to your answer, through individual purchases.
Description of the scenario
This net that you see [interviewer shows net] is not an ordinary mosquito net but treated with insecticide. By getting rid of mosquitoes
and other insects (bed bugs), it will protect you and your family members from mosquitoes and other insects when inside it, thus allowing you to have a good night’s sleep. In addition, it will also reduce the number of episodes of malaria in your household if your household members sleep under these each night. In some villages, use of TMNs would reduce the number of times someone in a household
gets malaria from once a year to once every 2 years, thus saving time and money for the household, which would otherwise have been
incurred on the treatment of that malarial episode. You know that most people suffering from malaria have severe headache and fever
for about a week and are unable to work for about 4 days. In very small percentage of cases, malaria leads to complications or death.
As it has insecticide, you may experience cold-like symptoms, e.g. headache, running nose, in the first week, but thereafter there would
be no symptoms. Hardly any complaints have been received from people who have used the mosquito nets. This insecticide is not
harmful even to children. As the effect of the insecticide wears out with time, it needs to be treated again every year, for which you
would need to bring your household nets to an agreed place, e.g. the village school. Remember washing of the treated nets reduces its
effect. You are also aware that there are other methods to protect yourself from mosquitoes/malaria.
The mosquito nets are available in different colours and standard size of 6 4 ft and should last for about 5 years. Keeping the above
description in mind and reminding yourself of your income, your other expenditure commitments and your household’s expenditure
on treatment of malarial fever, kindly answer the following questions, which enquire about your willingness to buy treated mosquito
nets.
a
NMEP has been renamed recently as the National Anti Malaria Programme (NAMP).
information concerning TMNs focused on: describing the
benefits, side-effects, compliance and alternatives, along with
a physical description of TMNs. It is important that accurate
and unbiased information is given so, for example, that
benefits are not over-emphasized at the expense of the
disadvantages of an intervention. Each respondent was also
shown a treated mosquito net and was reminded about
income constraints and their expenditure commitments prior
to giving values.
Respondents were then asked whether they were willing to
buy a TMN or not. Those who were not willing to buy a TMN
were asked if they would be willing to do so if the option of
paying in instalments were available. Those who said ‘yes’ to
either question were subjected to the elicitation questions. A
bidding format with three randomly allocated starting bids
(Rs50, Rs75 and Rs100) was used to elicit peoples’ values.
Each person was asked, for example, ‘Would you be willing
to buy one treated mosquito net for Rs75?’ The respondents
were also offered a ‘don’t know’ option in addition to yes/no.
This was done to ensure that respondents are not forced into
giving a yes or no response, recommended by Harris et al.
(1989) and NOAA (1993). Those who said ‘yes’ to the starting bid were then asked about a higher bid and those who said
‘no’ or ‘don’t know’ were provided with a lower bid and asked
the question again. After this second bid, the respondents
were asked for their maximum willingness to pay as an openended question. Figure 1 provides an example of the bidding
format used for the three starting bid vectors and shows that
WTP for TMN
No Don’t know a
(DK)
Yes
Starting bid vector
Rs50, 75, 100
Yes
No DK
2nd bid vector Rs100, 150, 200
Yes
Max WTP
Figure 1.
values
No DK
Rs25, 50, 75
Yes
Max WTP
No DK
Max WTP
Bidding format used for elicitation of willingness to pay
a variety of starting bids were chosen. This was because it
would allow a testing of, and control for, any starting point
bias, which is a commonly found bias in WTP studies
(O’Brien and Viramontes 1994; Russell et al. 1995; Stalhammar 1996).
The focus on the purchase of one TMN only was important
to ensure standardization of product across respondents.
Willingness to pay for mosquito nets
However, need and demand may differ between households,
as may the marginal utility of additional TMNs per households. Therefore we also asked respondents how many TMNs
they would buy at their maximum stated WTP as well as
checking the maximum they would be willing to pay to buy the
total number of TMNs needed for their household (if there was
a difference between need and demand at the price stated).
This also allowed us to check the reliability of WTP answers.
The final questionnaire comprised five main sections in the
following order: household socioeconomic and demographic
profile, use of preventive measures, treatment-seeking
behaviour, willingness to pay income and expenditure
patterns (Bhatia 2000). This sequencing was to help respondents consider the impact that malaria has on their lives prior
to answering any valuation questions. It also ensured that the
framework for thinking was the household. Household
income and expenditure questions were asked last in case
they had an adverse impact on responses (at least all the other
information would have been collected by this point of the
interview).
Sampling
The sampling frame for our part of the study included the 42
villages in each arm of the trial. It also included all other
villages in Surat outside the trial area (OTA) that had a high
incidence of malaria (Annual Parasite Index >2.5) and were
at least 5 km away from the nearest trial village – a total of
336 villages. Villages were selected from outside the trial
area in order to compare the results with villages in each
intervention arm. This was essential because we expected
the trial itself to influence stated demand (either because of
changing perceptions or need for mosquito nets, as villages
in one arm were provided with nets) and we needed to
inform policy-makers of likely demand for people outside of
a trial setting. Twenty villages from each of these groups
were selected randomly, making a sample of 80 villages in
total. In seeking respondents for the survey, interviewers
were instructed to visit the home three times in search of the
main earner of the household and if on the third visit they
were absent then to interview another adult (with preference
for the housewife or parents).
The sample size for households was calculated three ways:
using the sample size tables provided by Mitchell and Carson
(1993),3 based on the proportion of people willing to buy
TMNs from a similar study in Orissa, India (Rath 1994), and
using the mean WTP values obtained from our qualitative
research. The largest sample size required 300 households per
group. As there were four groups (three within the trial and
one outside the trial area), the total sample size was 1200
households.
Organization of fieldwork
A team of eight field investigators, three research assistants,
one assistant research officer and two data entry operators
were employed. All the research staff recruited had university
level education and were provided with the necessary training in both the quantitative and qualitative methods that were
405
to be used for the study, and were trained in taking notes of
responses, as well as observing and documenting non-verbal
actions.
Data obtained from the field were checked and coded at the
local level. To ensure the quality of data entered, double
entry was undertaken for all household interviews by two
data entry operators using FoxPro version 4.0. In addition,
verification of data entered was carried out by analyzing the
printouts of the data base files and from the preliminary
analysis of data (single frequencies) using SPPS PC+ version
7.0.
Results
Description of sample
The response rate was 100%. Of the 1200 respondents, 89%
were the main earners of the household and 87% were men.
Forty-eight per cent had no formal education and only 2.3%
of the respondents had higher education (i.e. graduation and
beyond). Manual labour was the most common occupation
reported (45.4%) followed by agriculture (23.4%).
The demographic variables of households showed that there
were an average of 5.12 (s.d. = 2.26) people in each house. The
majority of households were Hindus with less than 10%
stating they were Christians. With regards to the caste, almost
75% of the households belonged to the ‘Schedule Tribe’ followed by ‘Other Backward Caste’ (17%), ‘Other castes’ (6%)
and ‘Schedule Castes’ (3%). The Schedule Tribe was the
dominant caste, with Gamits and Halpatis accounting
together for more than 70% of this group.
Table 1 shows the characteristics of respondents and households by trial arm. It can be seen that, despite the randomization of villages, there were statistically significant differences
in characteristics of respondents (e.g. percentage literacy and
labourers) and households (e.g. percentage schedule caste,
type of house and ownership of land). The distribution of the
principal economic variables showed that the mean per capita
income per household was Rs5354 (s.d. = 999) with a skewed
distribution to the right. The mean per capita monthly income
was higher among IRS and EDPT groups compared with
TMN and OTA groups.
Willingness to pay results
The first WTP question asked respondents whether they
would be willing to buy a TMN. Seventy-nine per cent said
they would and 21% said they would not be willing to buy.
The main reasons people said they were unwilling to pay
were: no felt need, no money, the belief that the government
should provide free TMNs, and because using mosquito nets
was considered uncomfortable. Table 2 shows how many
people said ‘yes’ to the different starting and progression
bids. It shows that the higher the starting bid, the lower the
number of people who said they were willing to buy and vice
versa, and that this pattern continued with the follow-up
bids. This observation was statistically significant (χ2 test; p <
0.001).
406
MR Bhatia and JA Fox-Rushby
Table 1. Respondent and household characteristics by study arm
Respondent and household characteristics
TMNs
Respondent’s gender
% male
Respondent’s education
% literate
Respondent’s occupation
% labourers
Household’s caste
% Schedule tribe
Type of house
% Kacchaa
Ownership of irrigated land by household
Household’s religion
% Hindu
Livestock owned by household
% bulls/cows
Mean household size
Mean per capita monthly income
IRS
EDPT
OTA
p-value
0.145
89
83
89
86
50
57
45
57
56
42
40
44
85
64
72
77
72
17
53
34
69
35
69
30
87
94
89
88
47
4.8
503
50
5.2
586
57
5.1
635
54
5.4
415
0.004
0.0001
0.001
0.001
0.001
0.02
0.06
0.0032b
0.037b
TMNs = treated mosquito nets; IRS = in-house residual spraying; EDPT = early diagnosis and prompt treatment; OTA = outside trial area.
a House built with mud and hay.
b p-values obtained using one-way ANOVA; χ2 test used for others.
Figure 2 shows the histogram of all the final maximum values
given. It can be seen that the distribution is not normal and
that around 20% of responses were zero. There is also a
clustering of values around Rs50, Rs75 and Rs100. It was
observed that more than 80% of those respondents who were
willing to pay something to a follow-up bid stated that the
highest offer bid they accepted was their maximum willingness to pay.
Table 3 shows the percentage of zero values and mean WTP
values and ‘need’ by trial arm. It can be seen that almost half
of the households (47%) belonging to the TMN group quoted
zero values. This was statistically significantly higher
(ANOVA, p < 0.001) when compared with other arms of the
trial. There was no statistically significant difference between
the mean WTP for one TMN among the trial arms, when zero
values are excluded (Rs73). However, the mean WTP for one
TMN is statistically significantly lower (ANOVA, p < 0.001)
in the TMN group (Rs39) compared with other arms when
zeros are included. On average the number of TMNs
needed is greater than the number of TMNs the households
are willing to buy at the quoted price in each study arm.
Table 2. Summary of results for willingness to pay by starting bid in Indian Rupees, 1997
Starting bid
(no. asked)
Answer
No. replied
2nd bid offer
(no. asked)
Rs100 (308)
Yes
110 (35.7%)
Rs200 (110)
No
DK
197 (64.0%)
1 (0.3%)
Rs75 (198)
Yes
206 (65.8%)
Rs150 (206)
No
DK
105 (33.5%)
2 (0.6%)
Rs50 (107)
Yes
291 (90.4%)
Rs100 (291)
No
DK
30 (9.3%)
1 (0.3%)
Rs75 (313)
Rs50 (322)
DK = don’t know.
Rs25 (31)
Answer
No. replied
Yes
No
DK
Yes
No
DK
Yes
No
DK
Yes
No
DK
Yes
No
DK
Yes
No
DK
9 (8.2%)
101 (91.8%)
0
122 (61.6%)
75 (37.9%)
1 (0.5%)
8 (3.9%)
198 (96.1%)
0
89 (83.2%)
16 (15%)
1 (1.9%)
235 (80.8%)
56 (19.2%)
0
28 (90.3%)
2 (6.5%)
1 (3.2%)
Willingness to pay for mosquito nets
407
400
(15%). Respondents also stated that the need for TMNs was
greatest during July to October when almost half of the
respondents (48%) preferred to buy.
300
Prevention methods
200
100
0
0.0
50.0
25.0
100.0
75.0
150.0
125.0
200.0
175.0
250.0
225.0
300.0
275.0
Figure 2. Histogram of household’s maximum willingness to pay
for one mosquito neta (mean = 57.4, s.d. = 38.9, n = 1196.0)
Comparing across study arms, it can also be observed that the
relative need for TMNs is significantly lower among the TMN
group, as is the maximum WTP for all TMNs.
Seventy per cent of those willing to buy TMNs said they
would prefer to make a one-time payment for their TMNs,
with 30% preferring to pay in instalments. The expected
sources of money for paying for TMNs included using available cash (58%), savings (27%) and borrowing the money
Figures 3 and 4 show the preferences for, and use of, alternative approaches for preventing mosquitoes. It shows that
although the majority of the respondents preferred TMNs as
a mosquito preventive measure, very few actually were using
TMNs. Instead, the majority were using smoke and bedsheets. The preferences and use of alternative approaches to
preventing mosquito bites were statistically significantly
different across arms of the trial. The relatively high use of
TMNs in TMN villages compared with other arms was
because TMN villages were provided with project TMNs free
of cost. Forty-two per cent of households owned at least one
mosquito net. The mean price paid for their untreated net
varied from Rs86 in the EDPT group compared with Rs141
in the IRS group.
Most respondents (97%) knew that a mosquito bite could
cause disease and many (76%) felt mosquitoes were a major
nuisance. This knowledge was consistently more than 90%
across all arms of the trial. On probing the 1163 respondents
who knew that mosquitoes cause disease, malaria fever was
most frequently mentioned (85%). Other conditions mentioned were skin rash, allergy, itching and boils.
Treatment-seeking behaviour
We also asked about the household’s treatment-seeking
behaviour if they reported a household member having had
malaria within the last month. Three hundred and eight
Table 3. Description of main results for willingness to pay (WTP) for one treated mosquito net, by trial arm in Indian Rupees, 1997
TMNs
Zero WTP values
%
WTP for one TMN
Mean
s.d.
WTP for one TMN (excluding zero values)
Mean
s.d.
No. nets willing to buy at maximum stated WTP
Mean
s.d.
Number of nets needed per household
Mean
s.d.
Maximum WTP for all nets for householda
Mean
s.d.
Sample size
IRS
EDPT
OTA
Total
p-value
47.0
12.4
12.5
14.0
21.4
0.001b
39.0
41.6
65.0
37.8
65.0
33.7
62.0
36.1
57.4
38.9
0.001
73.3
27.1
73.6
31.0
73.3
25.1
72.2
28.0
73.1
27.9
0.9417
1.29
1.6
2.23
1.4
2.21
1.3
1.92
1.3
1.92
1.45
0.001
1.8
0.38
2.7
0.80
2.7
0.78
2.6
0.86
2.43
0.87
0.001
92.4
118.0
300
158.0
116.0
299
158.0
109.0
297
134.0
108.0
300
135.7
115.8
1996
0.001
TMNs = treated mosquito nets; IRS = in-house residual spraying; EDPT = early diagnosis and prompt treatment; OTA = outside trial area.
a This maximum is not a simple multiplication of mean WTP for one net and mean WTP. The value is elicited from a direct survey question.
It differs for one of two reasons; either respondents were inconsistent or they reflected diminishing marginal values for additional nets.
b Except for zero WTP values where χ2 was used, all other p-values reported are obtained from one-way ANOVA.
1UK £ = Rs59.
408
MR Bhatia and JA Fox-Rushby
00
No. of households
Preventive measures
300
Fan
Smoke
200
Bed-sheets
Coil/mats
100
Spray
Mosquito nets
0
Tr
e
Ca
Sp
ra
ate
Ou
se
tsi
yv
de
de
dn
illa
tria
tec
ets
ge
tio
l (O
s(
(T
n
TA
MN
IR
(E
S)
)
DP
s)
T)
Intervention groups
Figure 3.
Preference for mosquito preventive measures by trial arms
No. of households
400
Preventive measures
300
Mosquito nets
200
Coils
Smoke
100
Bed-sheet
0
Fan
Tr
e
ate
dn
ets
Sp
ra
(T
Ca
se
yv
illa
ge
MN
s)
s(
IR
de
Ou
S)
tsi
tec
tio
de
n(
E
tria
l (O
DP
T)
TA
)
Intervention groups
Figure 4.
Use of mosquito preventive measures by trial arms
people belonging to 271 households reported malaria5 of
whom 24 had been admitted for treatment. The mean age of
the family member was 27.6 years (median = 28, mode = 40).
The number of malaria cases varied between the arms of the
trial with least number of cases belonging to the TMN group
and maximum cases reported from OTA villages. This difference was statistically significant (χ2 test, p < 0.001).
The sources of treatment also varied between trial arms (see
Figure 5). For example, use of the private sector ranged from
18% in the EDPT group to 37% in the IRS group. In spite of
this variation, the private sector was an important source for
treatment in all trial arms, next only to the project workers.
In the absence of project workers, high utilization of the
private sector was also observed in villages outside the trial
areas.
On the aggregate level, almost equal numbers (31%) sought
treatment at private clinics and from the project workers.
About 21% took treatment at home or consulted the bhagat
(traditional healer) and only about 17% sought treatment
from the government health sector. Only 40% of those
Willingness to pay for mosquito nets
409
No. malaria cases
120
100
80
Treatment source
60
Others
40
Private
20
Govt
Home/Bhagat
0
Tr
e
ate
Sp
Ca
dn
e
ra
ts
yv
il
(T
se
MN
lag
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Intervention groups
Figure 5.
Sources of initial treatment for malaria illness by trial arms
reporting malaria fever sought subsequent treatment. Of
these, the majority (75%) sought treatment at private
facilities.
As the TMN, EDPT and IRS groups were all given a project
worker for early diagnosis and treatment, we examined
whether there were differences between the trial and nontrial groups as a whole. The findings showed that there were
statistically significant differences in mean number of cases,
severity of malaria in terms of admission and length of hospital stay, and household days lost – all of which were higher
outside the trial area compared with trial villages. For
example, the mean number of days admitted as a result of
malaria illness varied from 1.6 in TMN villages to 5.3 outside
the trial area (ANOVA, p < 0.05).
Discussion
This study reports the best possible response rate to a survey
– 100%. Although the majority of the respondents said they
would be willing to buy at least one TMN, around 20% were
not willing to buy (even with the offer of paying in instalments). The vast majority of those who said they were not
willing to buy (55%) belonged to the TMN arm of the trial,
and had already been given sufficient TMNs for free by the
Malaria Control and Research Project. However, this still left
around 10% of the entire sample unwilling to pay anything
for TMNs.
The mean WTP for one TMN was Rs57 (s.d. = 39) for the
study population as a whole and Rs73 (s.d. = 28) for those
willing to buy TMNs. Whilst the WTP was significantly lower
for the group, which had received TMNs, there was no significant difference in WTP between trial arms once the zero
values had been excluded. The average number of TMNs that
households were willing to buy at the mean WTP was 1.92
(s.d. = 1.45) and this differed significantly between groups.
Not surprisingly the TMN group was lowest, although on
average a household was WTP for 1.3 out of the 1.8 TMNs
they felt they still needed. The stated demand for TMNs was
significantly higher in the EDPT, OTA and IRS groups (mean
= 2.43, s.d = 0.81).
Variability of independent variables, both economic and
other taste and preference variables, was observed across
trial arms. For example, the preference and use of TMNs as
preventive measures was the highest in the TMN group.
Similarly, although the preference for mosquito nets was
high in all the groups, their use was very low in all groups
except the TMN group where project nets were distributed.
Other variables like per capita monthly income and ownership of irrigated land were higher in the IRS and EDPT
group.
The findings of this descriptive analysis have a number of
implications for further data analysis. The most important
next step is to begin to understand what causes the variation
in stated amounts of WTP. For example, what factors other
than perceived need of TMNs makes people unwilling to buy
any TMNs? And of those who are willing to pay, what characteristics are likely to lead to high and low values?
In terms of the design of future studies using the bidding
format, the role of the final WTP question needs to be discussed given that a large number of respondents quoted the
bid price. This could depend upon the perspective of the
study. If a WTP study is undertaken from a valuation perspective as in cost–benefit studies, then the final maximum WTP
question may still be justified provided the final value is not
framed by the second bid value. However, as 80% of those
who were willing to pay did not give higher values than the
offer bids, this should be questioned and researched. It may,
for example, point to the need to consider alternative forms
of elicitation mechanisms. Alternatively if the pricing
perspective is considered, then the role of the final WTP question is hard to justify as a majority of the respondents quoted
the bid price and the expectation is only to identify the proportion willing to buy at a particular price. If these prices are
below expected costs then a higher final bid value should be
used.
410
MR Bhatia and JA Fox-Rushby
A number of policy implications emerge from this study.
First it confirms that the majority of the households are
willing to buy TMNs and suggests that at a mean WTP of
Rs57, 649 households would buy at least one TMN. This
information, coupled with the cost of providing and distributing TMNs, could assist policy-makers in taking pricing
decisions and gain an idea of any subsidy required to implement this programme at different levels of coverage. At this
stage it is notably lower than the average paid for untreated
nets, although this does not account for the size of the
untreated nets. However, further analysis is needed to determine the relationship between coverage and price levels set
for TMNs for different groups. Similarly, further analysis to
understand the inter-relationship of variables is necessary
before concluding which types of characteristics are the most
important explanators of WTP. Given that there are significant numbers of respondents not willing to buy TMNs,
policy-makers need to consider the potential role of exemption mechanisms and inducements of consumers into the
market in the event charges are introduced for a TMN programme, and further analysis may help to determine which
characteristics of households could lead to the most appropriate methods of targeting any exemptions and market
inducements.
This study also suggests two ways of increasing demand in
relation to the running of a TMN programme. For example, a
significant proportion (30%) of households who are willing to
buy would prefer making payments in instalments. This may
ensure greater coverage and make TMNs affordable to those
who may not be able to raise the capital otherwise. Secondly,
there appears to be a conflict between the time when the
households would need TMNs and the time when they would
have most money available to buy them. Forty-eight per cent
of the respondents were more willing to buy during July and
October, when the need for TMNs is greatest, but these are
the months when the agriculturist has little spare money as it
is needed to invest in their land and, at the same time,
employment opportunities for agricultural labourers are
scarce. Our survey took place in the months June to September, when the mosquito nuisance is high.
Both the methods used and the results of this study suggest
findings from other WTP studies need to be considered more
carefully if WTP studies are to have an appropriate impact on
policy making. One study in the literature has reported mean
WTP for TMNs in India (Rath 1994). The Orissa study
reported a mean WTP of Rs150 per TMN compared with
Rs57 in our study. This high WTP reported in Orissa is difficult to account for. Malaria is a major public health problem
in both Orissa and Gujarat, and although the magnitude of
problem is greater in Orissa compared with Surat, it is
unlikely to explain the three-fold differences in WTP. For
example, it is unlikely to be justified on the grounds of
income, as rural Surat is much richer than rural Orissa. A
potential explanation could be the difference in methodology. The Orissa study used open-ended questions, which are
notorious for exaggerated WTP values (Mitchell and Carson
1993; NOAA 1993; Russell et al. 1995), and secondly it
elicited values in open meetings, which may have resulted in
more socially acceptable responses. However, it is interesting
to note that the decision was made to sell TMNs in Orissa at
Rs50 (Thomas 1997), which is more consistent with our estimates.
Finally, it was heartening to learn that it is possible to undertake a WTP study in a rural setting of a developing country
with a high response rate as well as reasonably realistic estimates of WTP estimates. Much of this, it has to be said, was
due to training as well as the excellent and hardworking interviewers. The bidding format, which is considered to be a more
complex elicitation method requiring skilled interviewers,
was well received by the respondents as bargaining was commonly observed in the market place. The qualitative phase
prior to the household survey proved particularly useful in
setting realistic bid prices. If we had to change anything for a
future survey of hypothetical willingness to pay, it would be
making further refinements in the scenario, attempting to
make the instrument simpler, and considering whether other
elicitation mechanisms or alternative higher bids would
significantly change the results.
Conclusions
WTP studies have an important role to play in influencing
pricing policies, particularly in a developing country context,
where such studies are mainly undertaken from a pricing
perspective. However, until recently, there existed no guidelines for undertaking WTP studies in health sectors of
developing countries for pricing or as a method of valuing
benefits. This paper adds to the recent effort expended by
Whittington (1998) and others towards developing guidelines
for undertaking WTP work in low income countries by providing insights into the design and analysis of a WTP study,
and sharing some of the experiences in implementing such
studies.
This study has shown that it is possible to undertake WTP
studies in a rural setting of a developing country for a health
care good. To increase the reliability and validity of WTP
estimates, it is recommended that future studies include
qualitative research methods as a part of the overall methods
and that efforts are expended in developing the appropriate
scenario. The main empirical results showed that WTP
differed significantly, along with several socioeconomic,
demographic and malaria-related variables, across the trial
arms of the study. Future research on WTP studies for the
same good (i.e. TMN) using different elicitation questions
and for different health care goods are recommended to
establish the reliability and validity of WTP in a developing
country setting.
Endnotes
1 Caste and tribes: In the hierarchy of the existing caste system,
Schedule Tribe and Schedule Castes are on the lower end and so
have special provisions in the Constitution of India. The Government of India aims to promote their welfare through various
developmental programmes. Schedule Tribe members are those
residing in remote areas that have remained out of touch with civilization. Gamits and Halpatis are important sub-castes within Schedule
Castes and are in significant numbers in rural Surat.
2 Selected from a range including: open- or closed-ended ques-
Willingness to pay for mosquito nets
tions, dichotomous choice with follow-up, a payment scale and
bidding games (Donaldson et al. 1998).
3 For a 5% level of significance and with a 90% power to show
a difference of 40% or more between two groups, the required
sample size is 290 households per group, assuming the coefficient of
variation = 1.
4 1 UK £ = Rs59 (1997).
5 Fifty-six per cent of these were reported to be clinically diagnosed by a doctor and in about 10% of cases through a laboratory. In
all other cases, it was based on the respondent’s opinion.
411
Stalhammar N. 1996. An empirical note on willingness to pay and
starting point bias. Medical Decision Making 16: 242–7.
Thomas K. 1997. Evaluation of the process of demand generation for
insecticide treated mosquito nets. In: Rath AD, Pet I (eds).
Approaches to increasing the use of insecticide treated mosquito
nets in Orissa, India. Proceedings of the round table meeting.
Whittington D. 1988. Administering contingent valuation surveys in
developing countries. World Development 26: 21–30.
Acknowledgements
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This work is a part of the Malaria Control and Research Project, a
bilateral project between the Government of UK and the Government of India. We acknowledge this research was funded by the
Department for International Development (DfID) of the United
Kingdom. However DfID can accept no responsibility for any information provided or views expressed. We thank Dr David Evans
(WHO) and Dr Marcia Weaver (USA) for feedback on the WTP
instrument. We acknowledge the efforts put in by the research staff
during data collection and data entry operators, in particular Mr
Umesh Rathod and Mahesh Chauhan. We are extremely grateful to
the people of the study villages for sharing their information with us
and for their time for focus group discussions and in completing the
household survey. Finally, we thank the two anonymous referees for
their very helpful comments.
Biographies
Dr Mrigesh Bhatia is a lecturer in health policy and course director
for the MSc in International Health Policy, in the Department of
Social Policy at the London School of Economics. He is medical
graduate with an MD in Preventive and Social Medicine and a Ph.D.
in Health Economics. His research interests include economic evaluation of health care interventions and aspects of health sector
reforms in low-income countries.
Dr Julia Fox-Rushby is a senior lecturer in health economics. She has
written numerous academic papers on the cost-effectiveness of
health interventions across the world, specializing particularly in
maternal and child health, malaria and, more recently, vaccine preventable diseases. She has also been involved over the past 15 years
in developing a number of non-disease specific measures of healthrelated quality of life as a member of the EuroQol group, advisor to
the WHOQOL group and as principal investigator of the KENQOL
group.
Correspondence: Dr MR Bhatia, Department of Social Policy,
London School of Economics, Houghton Street, London, WC2A
2AE, UK. Tel: +44 207 955–6416; fax: +44 207 955–7415; Email:
[email protected]