NON – PROBABILISTIC SAMPLING USE IN QUALITATIVE MARKETING
RESEARCH. HAPHAZARD SAMPLING. VOLUNTEER SAMPLING
Gabor Manuela Rozalia
“Petru Maior”University of Tg.Mureş, [email protected]
According to marketing, the firm should focus on the market, to a market for it, it should involve in the
economic-social environment structures, it should syncronize its activity with the dynamism and directions
enforced by this environment development. To achieve all this, the firm needs permanent information, that is
increasingly considered lately as being an implicit part of the modern firm’s resources along with its human,
material and financial resources. Intuitive, subjective factors appear in the market research (and they have a
major significance) and in designing a market research it should take into consideration not only consumers’
requirements but their wishes and aspirations as well, things that are less “measurable”and are more difficult
to implement mathematically or statistically but with a major importance for the firm.. A market research based
on non-probabilistic sampling methods may provide relevant and valuable information about the consumers’
wishes, about their expression ways (wishes related to existing products and future wishes as well) and the same
are those providing the objective side in taking decisions by the firms’ managers.This paper describes two types
of non -/ probabilistic sampling wich can be used with succes by the romanian firms in marketing research.
Key words: non – probabilistic sampling, convenience sampling, volunteer sampling
1. Non – probabilistic sampling, theoretical and practical issues
The non-random sampling is found in specialty literature with various names, non-probabilistic sampling,
oriented sampling, empiric sampling, subjective sampling respectively but all refer to the same principle i.e.
the national and voluntary selection of sample units respectively, nevertheless adapted to the established
sampling type.
The non-random sampling, is less stringent, is easier to apply, it does not involve taking
representativeness into consideration as the desirable purpose for the sample description. These sampling
methods usually leave the researcher to decide which of the investigated population components will be
selected. As the case stands, schemes in this category are prevailingly used in case of exploratory research,
examination and research carried out by the method of observation and qualitative research.
Therefore, in the practice of statistic sampling, a series of non-random methods has developed depending upon
statistic population features and research objectives. These are also called techniques of rational choice or
“pragmatic sampling”. The main feature of these sampling methods is provided by the “rational choice” of
units that are subject to statistic observation. These methods are focused on assuring the sample
representativeness in relation to the reference population structure using a series of key features. The selection
of features is motivated by available information, as well as their implications within the research. The sample
representativeness is driven by the sample volume, and by the quality of data series related to the features used
to determine the population structure. Typical to these methods is that a sampling base is not necessary and the
probability that population units belong to the sample is not taken into account.
To set the sample, variables that are determined by several factors are chosen: research objectives, variables
chosen should be in correlation with variables studied, distribution of variables in related population must be
known accurately.
The advantages and disadvantages following the application of non-random techniques are presented in tabel
no. 1:
Table no. 1
Advantages
Disadvantages
1.They can be used succesfully when we have no access (or
1. As units are included in the sample
there is not) to a list of the studied population (for instance, there arbitrarily, probabilities of units to access the
is not a list of those who prefer sandwiches)
sample cannot be calculated. As the case
955
2. It is the only method that can be used when the target
population is hard to be identified (hackers) or is very specific
(for instance, the executive directors hired in major companies,
software engineers etc)
stands, the variance and estimator movement
cannot be calculated
3.A sampling base is not necessary
2. Because of the manner of unit sampling
from the sample, there is no guarantee that all
the simple units of population have the chance
to access the sample
4.They are less expensive than the random ones
5. Allow to achieve the results more quickly than the others
6. It can be adapted in the run when the research topic is difficult 3. A distorted sample can be generated
There is not a calculation formula to set the size of such a non-random sample, but, especially in qualitative
research, it can be gradually improved, and results are also analysed gradually. When the last selected units do
not bring new information, useful to study any longer, we can deduce that our sample is saturated and research
is completed.
Of the methods in this category, the rational techniques of generating a sample most used, the following can be
mentioned (figure 1): quota sampling, routes method, vaolunteer sampling technique, street surveys, random
sampling, “ad – hoc”sampling, expert sampling, network sampling (snowball) etc.
As the variance and estimator movement is not calculated, the only way to evaluate the quality of data
obtained is to compare them with data existing from a former observation or from another sampling. These
techniques provide results close to random sampling, if population is homogenous, and the research (operator)
intervention în establishing the sample is irrelevant.
„Snowball” sampling
Conventional sampling
Standardized sampling
Type units procedure
Self-sampling
Evaluative sampling
Nonrandom
sampling
Quota sampling
Volunteer sampling
Routes sampling
Haphazard sampling
Figure no. 1 – Main non-probabilistic sampling methods
It is the sampling method most used in market surveys according to several specialists, and is considered as
being specific to exploratory sampling. Compared to random sampling it was noticed that it requests lower costs
but, for a successful method, in the process of unit selection it is recommended to use some experts, insiders of
the studied population, and the profound knowledge about population and particularly of population uniformity
rate. It is also recommended when, there are such kind of situations in the marketing practice and it is
impossible to meet the conditions of performing a random sampling.
2. Haphazard sampling (convenience or haphazard or accidental sampling)
The principle of respondents’ haphazard sampling, consists of selecting deliberately units from the
interesting population, available at a given moment and in a certain place. For instance, in a shop only people
956
who are willing to provide the time necessary to fill in the questionnary related
related to sampling are interviewed i.e.
students in the first year who attend their classes, people at the cinema, the first ten cars entering a parking, the
first ten people attending a tournament, women placed in the first row at a concert, the first one hundred buyers
entering a supermarket department etc.
The most common method is street interviewing of people, the representativeness rate depending on the time
when selection is done, on location, being able to predict in certain situations the respondent
responden probability of being
selected, for instance of those who live or work in the area where selection is done.
Figure no. 2 – Haphazard or convenience or accidental sampling
In marketing, this sampling type is used for testing a questionnary prior to its application in general population,
population
in explorative research or as a preliminary research.
One of the reasons for which this sampling is used is that, apart other sampling types, and especially the
probabilistic ones, haphazard sampling is easy to implement. For instance, to evaluate a program
pro
for parents, we
may select a sample made of availability and accessibility concerning employed mothers, housekeepers, single
mothers, young mothers (teenagers) and those with more than three children, thus getting different opinions.
This sampling typee is recommended in the exploratory stages of marketing surveys and may be the generation
base of work hypothesis for actual sampling.
2. Volunteer sampling
The principle of this sampling type is self-selection
self selection of statistical units in sample whose main
mai advantage is the
fastness of building the sample but that satisfies the representativeness requirement very seldom, the researcher
having a low control over the sample.
For the first time this sampling has been used for psychological research and for testing
testing pharmaceuticals where
practically the random principle of selecting the sample units is difficult and wrongful to use.
VVolunteer sampling is subject to error at the highest level of all non-probabilistic
probabilistic sampling types
due to the selection principle,
ple, respondents decide by themselves if they participate or not in sampling
respectively.
The advantages and disadvantages of this sampling are shown in Table no. 2.
Table no. 2
Advantages
Disadvantages
1. It allows collection of a significant 1. Abatement between the values of volunteer sample characteristics and
amountt of very low cost information those of population in general, may lead to distorted indicators
(various information)
2. Distorsion is higher than in case of previous random sampling
sampl
due to
the volunteer population character
2. It applies easily (practically there is
no rule to apply) and is cheap and
these are real advantages for small
firms.
3. People are quite different: some are more venturesome, others have
more liberal opinions,
nions, different educational and professional status, some
people have a higher need of affirmation than remaining population,
some have a lower authority, some are less conventional in aproach,
others are more sociable etc.
957
4.Error produced in these selections is mainly due to the higher
availability of some population members to participate in such sampling
3. Most times, in order to build the
sample, the researcher contacts his
friends, relatives, colleagues
5. It is necessary to check if there is any difference between volunteers
and non-volunteers
6. Those who offer voluntarily have further information about the topic
investigated by the non-volunteers
7. Sample non-representativeness
When making such sampling one may start from the assumption that, by volunteer sampling, the possibility of
entraining a great variety of people types occurs.
An increasingly used way of volunteer approached of students is posting of questionnaries on the internet and
this type of volunteer selection may drive a significant representativeness if more sources are used i.e. posting of
questions on various web sites implicitly driving the selection of some various people. The greatest advantages,
admitted by researchers, concerning respondent selection method i.e. the on – line method is speed, cost –
efficiency ratio – on average, an on-line sampling is cheaper by 30 % than phone sampling – and response rate
is high.
As a way of volunteer recruitment, the questionnary is published in daily newspapers, or it is distributed within
local organizations or community groups.
There are two main types of volunteers in literature:
Those who offered as volunteers before meeting the sampling operator; this category includes those
people who see an ad in a local newspaper where volunteers for a survey are required;
− Those who are part of a “captive” group, as usual family’s members, individuals in a waiting room in a
group practice etc. In these cases, the problem is if these people are real volunteers as most times,
people selected in this way do not reject their participation in sampling.
The main difference between self-sampling and haphazard sampling is that, in the first case, respondents are
asked if they want to participate in and only those who accept are interviewed, in the second case, respondents
located in a certain place and at a given moment are interviewed.
−
Conclusions
Intensive use of the non-probabilistic method of extracting units in sample is recommended for the market
survey taking into account that, in marketing, producers and service suppliers are aware of the consumers’ key
characteristics, those characteristics practically used for the segmentation related to products or product range.
Time and budget alloted to a market research have a major importance in marketing, and in market research
respectively, and most sampling types described in this paper meet these requirements.
In market research, significance is shown by quantitative variables and what any firm whose strategy is
market development and extension is trying to have, and having an as high as possible market share namely the
“measurement” of qualitative variables, consumers’ attitude intensity, opinions, intentions, reasons
respectively, this difficulty of measuring the market intangible characteristics is possible by means of nonprobabilistic sampling methods.
Literature
1.
1.
2.
3.
4.
3.
5.
6.
1. Andrei T. – Statistică şi econometrie, Ed. Economică, Bucureşti, 2003, p. 247
2. Cătoiu I. (coord.) - Cercetări de marketing, Ed. Uranus, Bucureşti, 2002
3. Gabor M. R. - Investigating method of decisions. “Snowball” sampling” , Al III-lea Simpozion
Ştiintific International de Statistică, nov. 2006, organizat ASE Bucureşti şi Institutul NaŃional de
Statistică, ISBN 973–594 –884–2, ISBN 978 – 973 – 594 – 884 -– 9
4. Hawkins D. I., Best - Consumer behavior: building marketing strategy, McGrow Hill,
R o. J.,Coney K. A.
New York, USA, 2001
958
4.
7. 5. Kitchenham B., - Principles of survey research. Part 5: populations and samples, Keele
8.5. Pfleeger S. L. University, Staffs, UK Arlington VA
9. 6. Moutinho L.,. - Analiza cantitativă în managementul marketingului, Ed. Tehnica – Info,
10.6.
Goode M., Davies F. Chişinău, 2005
11. 7. Olsen D.
- Marketing research: overview qualitative method, Department of Marketing,
12.7.
BBusiness Economics & Law School of Business, University of Alberta
13. 8. Thompson S. K. - Targeted rondom walk desing, Simon Fraser University, Survey
14.8.
Methodology, 2006
15.9.
9. Wilson Ian- Some practical sampling procedures for development research, University of
Reading
16.10.
10. www.bardwellconsulting.com
17.11.
11. www.socialreasearchmethod.net/ks/sampnon.htm
18.12.
12.http://www.wadsworth.com/psychology_d/templates/student_resources/workshops/res_met
hd/ sampling/sampling_29.html
19.13.
13. http://www.southalabama.edu/coe/bset/johnson/lectures/lec7.htm
20.14.
14. http://www.evaluationwiki.org/wiki/index.php/Survey_Sampling
21.15.
15. http://www.uow.edu.au/student/attributes/statlit/modules/module1/samptypes.html
959