THE NASHVILLE MORBIDITY SURVEY
by
A. L. Finkner, John Monroe and Jack Fleischer
Institute of Statistics
Mimeo Series No. 252
April 1960
Prepared for
The Air Pollution Medical Program
Public Health Service
United States Department of Health, Education and Welfare
under
Contract Number: SAph 70961
September 30, 1958
f'
THE NASHVILLE MORBIDITY SURVEY
I·
PURPOSE OF THE STUDY
The Nashville Morbidity Survey was designed to collect, by personal interview,
morbidity and mortality data from households in Nashville and certain areas around
NashVille.
The area included in the sample was comprised of specified Planning
Units which had been delineated for the year 1958 by the Advance Planning Commission of Nashville and Davidson County.
The survey was conducted in January, February, and early March, 1959, the
months during the year when smog frequently is present, so that the health information could be correlated with air pollution data collected at the same time by
the U. S. Public Health Service.
e
II
DESIGN OF THE SAMPLE
A.
Definition of the Universe:
1.
The universe consisted of 51 City Planning Units in the City
of Nashville and surrounding area:
Planning Units 12 through
57, 65, 66, 67, 73, and 74.
2.
Eligibility was restricted to individuals occupying quarters
where they live and sleep most of the time.
Specifically,
this definition excluded
a.
College students, either in dormitories or private quarters,
unless the family of the student (father and/or mother)
maintained a residence, of which that student was a part,
within the geographical limits of the study area before he
went to college.
b.
Families (wife/or husband and children) of married
students unless the student lived as a resident in
the study area prior to attending college.
c.
Resident personnel and wards (inmates) of institutions
and their families.
d.
Transients and paying guests of hotels, motor courts or
other tourist and traveler facilities.
(If a family
resided in a trailer from which the wheels have been
removed, and if it met all other eligibility requirements,
that family was included.)
B.
The Sampling Unit:
The sampling unit (SU) was an area segment (or defined as a specific strip
along a street) with an expectation of about one household per sampling unit.
For
all practical purposes, the sampling unit is an eligible household.
C.
Stratification:
Stratification was based on the estimated number of households in the
universe and the sample size.
Strata were created such that there was the same
number of universe sampling units in each stratum. :two sampling units were selected at random from each stratum for interview.
each stratum were contiguous.
Universe sampling units within
Strata were contained within the geographic limits
of a planning unit by adjusting the expected size of the sampling unit upward
slightly.
(That is, instead of the expected size of the sampling unit being one
household in a given planning unit, it could have been, for example, 1.2 or even
1.5).
This design was selected to maximize scatter and yet retain those properties
of random selection which will allow unbiased estimates of the variances to be
computed.
A further desirable feature of the design is that the sample is
3
self'...weighting, since the sampling ra.te was the same in every stratum.
D.
Sample Size:
To obtain the requested sample size of' approximately 3000 households,
1,516 strata were defined, resulting in a total sample size of' 3,032 sampling
units.
III.TIlE.SAMPLE DRAW
The total number of dwelling units in the area according to the latest avail:.able count f'rom the Advanced Planning Commission was 69,224.
The 1,516 strata
were allocated to each Planning Unit in proportion to the number of' dwelling units
in each.
(Several of the smaller Planning Units were joined with contiguous Plan-
ning Units.:)
In each stratum, exactly 45 SU's were assigned.
Thus the
lI
expected"
size of' the sampling unit varied slightly among the strata; f'or example:
Table 1.
Illustration of' the Assignment of Strata and Sampling Units
to Planning Units*
Planning
Unit No.
Number of'
Dwelling Units
Number of
Strata
Number of'
SU's
"Expected"
Size of' SU
12
886
999
2,287
1,331
19
22
50
29
855
990
2,250
1,305
1.03626
1.00909
1.01644
1.01992
1,914
1,148
42
25
1,890
1,125
1.01270
1.02044
69,224
1,516
68,220
1.01472
13
14
15
73
74
TOTAL
* The
-
complete table of assignment is found in Appendix A.
4
After the number of strata had been determined for each planning unit, two
sampling units were selected at random from each stratum;
were selected between 1 and 45.
.!.~.,
two random numbers
These were first located as to block by accumu-
lating the number of dwelling units by block in each planning unit.
The expected
size of the sampling unit was then multiplied by the random number to determine the
block location.
Once the block in which the sampling unit fell was located, the Planning Com·
mission map for that block was examined and the sampling units assigned to that .
block designated,
Beginning in the upper right hand corner of the map and counting
in a clockwise manner, the selected sampling unit was located.
was identified as follows:
This sampling unit
All households receiving mail at this address and
including all those up to, but excluding a second address comprised the sampling
unit.
Ordinarily, this would have been only one household, but it could include
less {vacant house} or more, if new dwelling units had been added since the latest
Planning Commission count.
The sampling unit and number were marked in red on 1 inch
The street address number was also indicated where available.
= 200-feet
maps.
An arrow indicated
the clockwise direction, up to the next dwelling unit.
IV
QUESTIONNAIRE CONSTRUCTION
The questionnaire is composed of questions submitted to the Institute of Sta-
tistics by the Department of Preventive Medicine at Vanderbilt University and the
Air Pollution Medical Program, Public Health Service, U. S. Department of Health,
Education, and Welfare.
The format was designed to provide for seven household
members and as many possible respondents.
reqUired additional questionnaires.
Households with more than seven members
The questionnaire was pretested in parts of
Davidson County not included in the universe studied.
5
The eligible respondent for each family unit answered all applicable questions
for all family members.
The eligible respondent was the person most familiar with
the health status of the family and, therefore, usually was the housewife.
The
thirty-eight questions in the questionnaire are divided into six sections, according to the type of information sought.
The six sections are:
a.
Identification and information about dwelling un! t
b.
Demographic characteristics of family members
c.
Medical histories of family members
d.
Residential and occupational data about family members
e.
Opinions on local health conditiona
f.
Selected socio-economic and miscellaneous information
for the household.
Three supplemental forms were designed to be used with the questionnaire.
The
illness form was to be completed for each separate illness of each indiVidual, the
accident form was to be completed for each accident of each individual, and the
authorization form was to be completed for each doctor consulted and for each
hospital at which an individual had been treated.
A copy of the questionnaire
and supplemental forms are attached as Appendix B.
v
INTERVIEWER HIRING AND TRAINING
Hiring of the interviewers was done in Nashville after a screening of applicants by members of the Institute.
The interviewers were housewives living in the
Nashville area, most of whom had had experience in interviewing.
Training school for the interviewers began on January 12 and continued through
January 16.
naire.
They were instructed in field procedure and the use of the question-
During the training period each interviewer did one or more practice inter-
views which were checked and returned to the interviewer with corrections.
One
J
6
training session was devoted to explanation of medical terms used in the questionnaire.
A copy of the Interviewer's Manual and copies of the flash cards used are
attached as Appendix C.
VI
(
FIELD WORK
A.
The Basic Sample
The field work began on January 19 and was scheduled to last six weeks ..
Illness of interviewers and weather delayed completion until March 11.
Assignments were made to the interviewers periodically, usually at the
beginning of each week.
These assignments' included a list of sampling units and
200': 1" scale blueprint maps showing the exact location of the dwelling units,
identified by house number where possible.
the sampling unit number.
Each dwelling wss also identified by
Adjacent dwelling units were also plotted and an arrow
was shown pointing in the direction of the second dwelling.
The interViewers were
instructed to interview all families* in the designated dwelling and all families
occupying dwelling units up to, but not including, the second dwelling unit.
assur!3d every household an opportunity of coming into the sample.
This
For multiple
dwelling units the interviewers were instructed on the procedure for identifying
the sample dwelling unit.
To assure a daily cross-section representation of the
city, the maps were grouped by sections and the weekly assignments were made from
each section.
Completed questionnaires were brought to the superVisors almost daily
and assignment maps were returned when the interviewers completed the assignment.
* For the purposes of this survey, a family is defined as a unit of husband and
wife and their unmarried children living with them, or any part of such a unit.
For example, a. household may be comprised of the head, his wife, their two
unmarried sons, one married daughter and her two children, the father and mother
of the head's wife, one maid, and one roomer. In this hypothetical household,
there are five families according to our definition.
7
For sampling units where an interview was not obtained, a questionnaire was handed
in with the sampling unit number and the reason for non-interview.
All question-
naires were checked in by sampling unit number as completed or with reason for
non-completion.
B.
Sub-Sample for Physical Examination
In conjunction with the health survey, a clinic for physical examination
of approximately 100 selected families was held at Vanderbilt University.
Origin-
ally this was a random selection with certain sampling units designated as those
in which the households were to be asked to Participate in this phase of the study.
This plan was not successful because of the small number of contacts made on the
designated households daily.
e
A new plan was devised whereby each interviewer asked the second family
interviewed each day to participate.
This plan elicited more acceptance but not
enough variety of family size, and the end result was that the first and second
families interviewed each day by each interviewer were asked to participate in the
physical examination.
During the period for the physical examination clinic, the interviewers
brought to the superVisors those questionnaires for the families who had that day
accepted the offer of the examination.
These questionnaires were edited with the
interviewer present so that any mistakes on the questionnaire could be rectified
irmnediately.
The edited questionnaires were then sent to Vanderbilt Hospital where
the final selection of families was made.
Originally five families were to be selected each day for a period of four
weeks.
Due to failure of some families to report for examination an excess of
families was scheduled daily to assure a minimum. of 5.
As a result, a total of
106 families actually participated in this phase of the study.
8
C.
The Authorization Sub-Sample
The authorization form that was a supplement to the questionnaire was
included to obtain authorization from the respondent to examine the medical record
of the family.
Before the field work began, it was discovered that the laws of
Tennessee made it illegal for anyone other than the head of the household to sign
for minors or any other adult.
Since obtaining the signature of the head of the
household would necessitate call-backs in most cases, the interviewers were instructed to obtain the authorization forms if possible at the time of interview, and,
if not possible, to make no more effort.
Due to the extra cost involved, it did
not seem advisable for the interviewer to make call-backs for authorization forms.
The decision was made to try to obtain authorization forms from a selected
group at a later date.
The selection of this group was a 10 percent random sample
of the original 3,032 sampling units resulting in a total of 268 households.
VII
THE SAMPLE CHECK
Each assignment map, as it was returned by the interviewer, was checked against
the log to see that no sampling unit had been missed.
In this way the 3,032 sam-
pling units were accounted for as they were completed.
As the expected size of the SU was slightly greater than one household, in the
3,032 SUls the "expected" number of households was 3,060. Two households were
"expected" in 28 SUls.
Table 2 presents the distribution of sampling units by
expected and actual size of sampling unit.
e
9
Frequency Distribution of Sampling Units and Total Households by Expected
and Actual Size of Sampling Unit
Table 2.
Size of SU
(No. of HH per SU)
0
Expected
No. of SUrs
No. of HH's
1
2
3,004
28
3,004
2,580
56
135
27
4
2
0
0
3
4
5
6
7
8
9
Total
3,060
3,032
Actual
No. of Eligible HH's
No. of SU's
0
282
2,580
270
81
16
10
0
0
1
1
8
3,032
2,974
9
The total number of SU's which deviated from Itexpectedll is 440, or 14.5 percent
of the total sample.
A distribution of these 440 showing the net loss from expec-
tation of 86 households is given in Table 3.
Table 3.
Distribution of Sampling Units and Households by Expected Size
of SU for Those SU's Deviating from Expectation
Size of SU
Expected
Actuai
I
0
1
1
1
1
1
1
2
2
2
3
4
5
8
9
1
.l
Total
No. of
SU's
No. of HH's
Lost
282
116
282
No. of HH's
Gained
Net
Loss
116
50
12
8
25
4
2
1
1
7
8
7
2
7
440
289
-2032
86
10
The "lost" households were due to the following situations:
No existing dwelling unit
135
Vacant dwelling unit
125
Student occupied dwelling unit
29
Total
289
Table 4 shows the interview status of the 2974 eligible sample households.
Table
4. Interview Status of Eligible Sample Households
Status
No. of Eligible HH's
Completed interview
Percent of Total
HH i S
~ligible
2,649
89.1
Failure to contact
171
5.8
Refusals
135
4.5
"Limit of 3" rule
15
0.5
Respondent failure
4
0.1
2,974
100.0
Total
A "No Contact" household is a household in which an interviewer was not able
to contact a person on three separate calls --- usually on different days of the
week and at different times during the day.
After the initial canvass according
to instructions, there was a total of 264 "No Contacts."
From these 264 house-
holds, a random sample of 100 was drawn for special completion efforts.
In these
100 households, eight interviewers were able to complete 85 interviews in less
than one week.*
* Of the 15 SU's not interviewed in the sub-sample, six were refusals and two
were found to be students. The remaining seven still could not be contacted
after intensive search. These seven were combined with the 164 not in the
sub-sample to make the 171 "No Contacts" shown in Table 4.
11
If a sampling unit was found to contain more than 3 households, the number
interviewed was held to 3 households selected at random from the total number in
the SUo
This "Limit of 3" rule, although arbitrary, was imposed to avoid excessive
interviewing loads in certain SU's, yet to provide reasonable estimates of that
sampling unit's characteristics.
Respondent failures are those households in which the eligible respondent was
incapacitated either through health, language difficulty, hearing or speech impediment.
There were 20 such cases after the initial canvass.
Since most of these
failures were due to ill health, it was decided to make another attempt to complete
an interview either with the respondent or some responsible adult in the failure
household.
One interviewer worked with the Public Health Nurse assigned to
Vanderbilt University by the Air Pollution Medical Program, Public Health Service,
on re-visits to the 20 households; 16 of the 20 were completed under these special
rules.
VIII
EDITING AND CODING
Completed questionnaires were edited daily by four supervisor.s to insure that
each one had been properly completed.
Questionnaires with mistakes or missing
information were returned to the interviewers for correction or completion.
The code was developed in consultation with the Vanderbilt study staff.
The
code and card layouts were planned so as to offer maximum coverage of responses in
keeping with the overall objectives, with groupings to permit generalization of
tabulation where possible.
The code being employed utilizes seven card sets; three sets for the basic
questionnaire, one each for Illness Forms and Accident Forms, one for the information on each death in the household, and one for residential history.
r
L,
12
The attached copy of the Code Manual (with code sheets) will indicate the
information coded on each card.
(See Appendix D.)
Most of the questionnaire presented few problems in the development of the
code because of the nature of the limited responses possible on any given question.
Through the use of the "yes
=1,
no
= 0"
code, the "yes" answers on any question
can be tabulated in the sorting process.
On Card I, the following "open-end" questions were included:
26b.
Why do you plan to move away from here anytime in the next year?
27b.
What health condition in this area of the city can you think of
that needs i~roving?
28b.
Why don't you think this area of Nashville is a healthy place in
which to live?
30b.
How are you bothered with smog in this area?
On these four questions the "a." part of the question was "yes" or "no" and was
not coded.
If the "b" partof the question was not applicable because of the
answer to "a. lI , "b." was coded as inapplicable ("y") in the space provided for a
substantive answer.
sorting step.
This procedure saves card space as well as an unnecessary
The code for these questions was based on a sample of the type of
J
answers which were being given.
These answers were put into generalizing cate-
gories which were felt to be most meaningful in the light of the general purpose
of the study.
On questions related to health condition (27, 28 and 30) space was
provided for the recording of two different responses if such were given.
On Card II, the code for "relation to head" is designed so as to categorize
relations with a one column sort on Col. 9 or detail on the two columns.
u_
Generally
except in the case of "Wife of head" (03), "Boarders and roomers" (91), "Hired
help" (92), and "Others" (93) --- this code utilizes even numbers for females, and
odd numbers for males.
The Occupational and Industry Codes are based on the
1,3
Classified Index of Occupation and Industries (Washington, D. C.: Bureau of the
Census, 1950).
Occupations and industries were grouped
80
as to provide maximum
use for socio-economic class information as well as similarity of duties and working conditions.
As a rule, a one column sort for each will provide information
of less detailed, but valid categories.
The Union Code is based on information
available in the Nashville Telephone Directory.
The "olJen-end" questions on
Card II were coded in the same way as those on Card I (26, 27, 28 and 30).
The questions coded on Card III were all of the limited response
tj~e
and pre-
sented no problems.
Card IV (Illness Form), for the most part was limited response.
The specific
illnesses were coded Within the framework of the International Cla.ssification of
Diseases: Vol. I (Geneva:World Health Organization, 1957).
available for consultation on classifying responses.
Local physicians were
The Hospital Code was obtained
from the listing in the Nashville Telephone Directory.
Card V (Accident Form) is essentially the same in material and layout as Card
IV.
Where applicable the same fields were used for comparable information.
Respon-
ses to question 1, "What Happeneu.?" were coded with the "External Cause" listing
of the International Classification.
Question
4, "What part of the body was
injured" (or 5b., "What did the doctor say the injurj7 was?" if necessary for
clarity) was coded with "Nature of Injury" listing of the
cation.
~.national
Classifi-
The code for question 2, "Where did it happen?" was developed in the same
manner as for other open-end questions.
Card VI is utilized for each entry for Question 17 (deaths in the household).
Most of the information to be coded fell within the framework of preVious coding.
The "Place of death" is coded with as much detail as is meaningful to the objectives of the study.
14
The coding on responses on residential history on Card VII is such that codes
established for Card I were sufficient
IX
f~r
this information.
PROCESSING THE DATA
Before,the data were transferred to punched-cards, some provision was made for
missing data.
The 85 questionnaires
compl~ted
in the random sample of "No Contacts" were
duplicated for the remaining 171 "No Contacts."
The 85 completed questionnaires
were ordered by SU number and marked to duplicate for the "No Contacts", also in
order by SU number.
Two duplications of one of the 85 questionnaires were
necessary to make a total of 171 duplications.
In limited number, completed ques-
tionnaires from Negro families were duplicated for "No Contacts" in other Negro
areas.
The 15 "Limit of 3" non-interviews were duplicated from the three completed
interviews within the same SUo
All four of the "Respondent Failure" non-interviews were due to ill health and
were considered to be more in the nature of refusals.
These four and the 135
refusals were not included in the data processing.
In a few cases, families, as defined for the purposes of this study, were not
interviewed.
In order to maintain the sample balance, these missing interviews
were duplicated from within the planning unit, controlling on age, sex, and color,
when known.
were made.
After each card set was coded and checked, listings of each card set
These are attached as Appendix E.
Tabulations submitted as interim
reports were based on the following numbers of cards in each set.
15
Card Set
No. of Cards
I
2J835
II
9J527
III
9 J4l7
IV
10J638
V
612
VI
344
VII
3J540
The following first run summaries were tabulated:
12.01
Number of Households Bothered by Smog by Planning Unit and Complaint.
12.02
Number of Households Bothered by Various Annoyances by Annoyance and
Planning Unit.
12.03
Number of Households Bothered by Various Annoyances by Frequency of
Complaint and Planning Unit.
12.04
Opinions About Health Conditions Needing Improvement by Health Condition and Planning Unit.
12.05
Opinions About Nashville as a Healthy Place to Live by Principal Detriment to Health and Planning Unit.
12.06
Opinions About Nashville as a Healthy Place to Live by Opinions About
Health Conditions Needing Improvement.
1.01
Condition of Building (Dwelling Unit) by Planning Unit.
1.02
Condition of Building (Dwelling Unit) by Census Tract.
1.03
Family Income Distribution by Planning Unit.
1.04
Family Income Distribution by Census Tract.
1.05
Distribution of Amount of Rent Paid by Planning Unit.
1.06
Distribution of Amount of Rent Paid by Census Tract.
1. 07
Number of Rooms per Household by Planning Unit.
1.08
Number of Rooms per Household by Census Tract.
16
1.09
Number of Rooms per Person by Planning Unit.
1.10
Number of Rooms per Person by Census Tract.
1.11
Frequency Distribution of Age, Sex and Race by Planning Unit.
1.12
Number of Individuals Interviewed by Date and Planning Unit.
1.13
Distribution of Socio-Economic Status for Households Responding to
Four Selected Items: Family Income, Source of Income, Education of
Head and Occupation of Head.
1.13a Distribution of Socio-Economic Status for Households Responding to
Three of the Four Selected Items: Family Income, Source of Income
and Education of Head.
1.13b
Distribution of Socio-Economic Status for Households Responding to
Three of the Four Selected Items:, Family Income, Source of Income
and Occupation of Head.
1.13c
Distribution of Socio-Economic Status for Households Responding to
Three of the Four Selected Items: Family Income, Education of Head
and Occupation of Head.
1.13d Distribution of Socio-Economic Status for Households Responding to
Three of the Four Selected Items: Source of Income, Education of
Head and Occupation of Head.
1.13e Listing of all Households Not Responding to Two or More of the Selected Items.
2.01
Total Reported Illness for Day of Interview by Age, Sex, Race and
Planning Unit.
7.01
Ability to Perform Present Activities by Age, Sex, Race, Planning Unit,
and Cause of Disability.
Copies of these tabulations are not included in the report because of their
volume and are not attached as appendices since they have already been submitted.
In addition to the tabulations listed, ratios were computed for estimating
the population in each Census Tract in the survey.
Since Planning Units and Census
Tracts failed to coincide, no direct expansion was possible.
The estimation was
further complicated by the fact that parts of some Census Tracts were not included
in our universe of inqUiry.
Households in such areas had no chance of coming into
17
the sample and, hence, had to be treated as non-respondents.
These results have
also been furnished prior to the submission of this report and are not included
herein.
X
ERRORS ARISING IN THE SURVEY
A.
Sampling Errors:
With a sample size of 3032 SU's, the sampling errors on estimates of the
various means,
total~
and ratios for the universe as a whole were expected to have
very small sampling errors and such was the case.
Estimates of totals and ratios
for a few selected items and estimates of their standard errors and coefficients
of variation for the universe of inquiry are shown in Table 5.
Table 5.
Estimates of Totals and Ratios for Selected Items, Estimates of their
Standard Errors and their Coefficients of Variation
Estimated
Standard
Error
Estimated
Coefficient
of Variation
66,195
525
0.79 percent
222,030
1154
0.52
II
8,100
173
2.14
II
78,975
493
0.62
"
Proportion of HH 1 s Bothered by Smog
.2307
.0036
1.56
II
Proportion of HH's With Telephone
.7506
.0082
1.09
"
Proportion of HH's With Running Water
.9164
.0089
0.97
11
Proportion of HH's With Inside Toilet
.8836
.0087
0.99
11
Estimate
No. of Eligible Households
No. of People in Eligible Households
No. of Deaths During Past 5 Years
No. of Employed Individuals
The totals were obtained by a direct expansion.
The sampling rate was exactly
1 in 22.5 in each stratum so the sample results, when adjusted for non-response,
18
were multiplied by 22.5.
(In the estimate of number of households no non-response
adjustment was necessary, since, even for refusals and failure of the respondent,
the household was able to be counted.)
Hence, the formula is given as
(1)
= 45
k
E
i=l
y
i
k
E
= 22.5
2
E
i=l j=l
yi .
J
where
N = No. of universe SU's per stratum = 45
i
2
Yi = E yij/n.
j=l
J.
n = No. of SU'sin the sample per stratum = 2
i
Yij = the observation on the j~ SU in the i th stratum.
The estimated variance of the total is given by
where
2
si
=
2
-
E (Y .. - Y.)
j=l
1J
J.
2
•
With only two SU's per stratum in the sample and a constant number of universe
SU's per stratum (45) formula (2) reduces to
2 = (
ST
22·5 )2 kE
i=l
since
2
E
j=l
_ )2
(y iJ' - Yi
(
Yil - Yi2
)2
19
It should be noted that in the computation of the estimates of variance, only
1227 out of the 1516 strata were used.
of a non-respondent in the stratum.
The other 289 strata were removed because
Hence, the estimate of the variance is not
unbiased from this standpoint but the bias is not likely to be serious.
The
finite population correction factor has been ignored.
The ratio estimates are known as combined stratum ratio estimates and this
estimate is given by
R
=
(4)
The x variable in all cases was number of households while the l variable was the
number of these possessing certain characteristics.
The estimated variance of a
combined stratum ratio estimate is approximately
2
sR =
...L
T 2
x
where
i:
~
- 2 Rs
ni
Tx = estimated total of households
2
2 = i: (
x ij - -Xi) 2
sxi
i=l
2
2 = i:
s yi
(Yij i=l
yi )2
2
=
i: (x
syxi
ij - Xi)(Yij j=l
Yi )·
Again, for·ease in computation, formula (5) reduces to
.1
YX1j
20
where
n =
2k = 2454 .
The variance of the ratio as computed above is the correct approach since the
number of households vary from sampling unit to sampling unit and, hence, are
random variables.
However, the sample was designed
80
that this variability would
be a minimum; further it was designed so that the size of the sampling unit was
approximately one househOld.
The reason for this attempt was that the Air
Pollu~
tion Medical Program wished to use the household as the observational unit in many
of their studies.
If the lIcluster" size is approximately one household, this can
be done without considering the influence of the intra-cluster correlation coefficient on the relationships derived.
It is therefore of interest to compare the
estimated variances or standard error of the combined stratum ratio with the standard errors computed by the binomial approach.
These comparisons are shown in
Table 6.
Table 6.
Comparison of the Standard Errors of the Mean Proportions Estimated
by Ratio and the Binomial Approach
Standard Error
Binomial
Ratio Estimate
Proportion of HH's Bothered by Smog
.0036
.0085
Proportion of HH's With Telephone
.0082
.0087
Proportion of HH's With Running Water
.0089
.0056
Proportion of HH's With Inside Toilet
.0087
.0065
The formula for the binomial was taken as
S
2 _ pn
P
-~
n
21
where
= proportion
q = proportion
=1 - P
p
n
with the characteristic
Without the characteristic
= total sam;ple size = 2454.
This formula, of course, ignores the effect of stratification; even so, the agreement is very close.
Since over 85 percent of the sampling units were one house...
hold in size, this result is not surprising.
to check the result for smaller sample sizes.
For this report, no attempt was made
However, it may be that the binomial
approximation would provide a quick and reasonably accurate estimate of the variance
for various sub-populations of interest.
B.
Coverage Errors:
No systematic quality check was attempted, but the results seem to indicate
There were 135 SU's where no dwelling unit existed at
that the coverage was good.
the time of the Visit and 125 SU's where the dwelling unit was vacant.
sample of 35
eu' 8
was drawn from the 135 and a random sample of 21 SU I S was selec-
ted from the 125 vacant HH's.
56 sampling units.
A random
A special interviewer was a.ssigned to check these
The results of his recheck showed the status of all 56 SU's
to be the Bame as those reported by the initial interviewer.
C.
Non-Response Errors:
As indicated in Table 4, information was not obtained from 325 eligible
sample households, or 10.9 percent of that group.
Also, as mentioned earlier, there
were originally 264 households in the "no contact" group.
A random sample of 100
of these 264 yielded 85 completions which we believe to be a representative sample
of the "no contact" group.
Expansion for this group was based upon the results of
the 85 responses rather than on the average of the 2,564 interviews obtained under
22
the 113 call-back" rule.
Similarly, the estimates for those interviewed under the
"Limit of 3" rule would seem to be adequate for those not interviewed under that
rule.
This leaves 139, or
responses.
4.6 percent, of the eligibles who are legitimate non-
It does not appear that any of the results would be seriously impaired
by assuming that the averages for the refusals would be the same as those for the
respondents.
This assumption is not true for the "respondent failures."
The
primary reason that a member of these households did not respond was because they
were physically or mentally unable to do so.
edly different from the respondent group.
Therefore, this category is undoubt-
However, the proportion of the total is
so small, less than 1/10 of one percent, that their exclusion has little effect on
the results.
D.
Response Errors:
This source of error is probably the most important of those mentionedj
and,unfortunately, less is known about it.
It encompasses such errors as memory
bias, prestige bias, unWillingness to disclose personal affairs, interviewerrespondent interaction and perhaps many others.
There are few techniques available
to measure the magnitude, direction or even the existence of response errors.
It
is always difficult and often impossible to obtain "standard" measurements against
which to compare the responses from a survey.
In this study, two possible checks were incorporated into the overall
design.
These were the authorization sub-sample and the physical examination sub-
sample.
In the case of the former, about a 10 percent sub-sample, the respondents
were asked to authorize an examination of medical records kept by their physician.
The medical records could then be compared with the survey answers.
The Institute
of Statistics did not participate in this examination and comparisonj hence, no
results of the check can be included here.
Although this procedure will undoubtedly
2'
disclose some information on the nature of response errors, it still leaves much
to be desired.
First, some individuals refused to authorize the examination of
their medical records; thus, the non-response bias here may be serious.
Second,
the respondent may have consulted a number of doctors and forgotten to give, or
deliberately withheld, the names of some.
Third, there may be a considerable
variability in the completeness of records among the physicians named.
However, it
appears that the discrepancies found will give a minimum estimate of the bias
involved.
Certainly, any information on response errors is valuable.
The second approach was also a sub-sample; a number of families were asked
to undergo a complete physical examination for each member of the family.
of 106 families actually cooperated.
A total
Here again the problem of non-response arises.
Although the examination undoubtedly gives an accurate picture of the respondent IS
current health status, it mayor may not disclose the health history.
Whenever
possible, it would be informative to compare the three sources of information for
the same respondent.
E.
Coding and Punching Errors:
Although the code was not overly complicated, it was qUite lengthy, and,
as shown in the previous
se~tion,
the magnitude of the job was quite large.
In
order to handle it expeditiously, a fairly large crew of part-time coders was employed.
Even though all coders were checked and each card punched was verified,
a number of errors still were found in the final listings.
Hence, it was impera-
tive that the listing be checked against the questionnaire entries.
This procedure
was chosen instead of checking against the code sheets since it was insurance against
both coding and punching errors.
Considerably more time was spent in preparation
for processing than had been anticipated, resulting in more expenditure of funds
than was estimated, but the effort in terms of both time and money seemato have
24
been worthwhile.
Since the questionnaires for the authorization sub-sample are
currently in Nashville, it was impossible to check them against the listings.
It
is recommended that this be done by the Air Pollution Medical Program before
analyses are run.
After corrections were made, the cards were again listed and the new
listings again checked against the questionnaires.
If the new listings agreed with
the questionnaires, the cards were re-inserted in the main deck which was then
ready for tabulation.
XI
COST ANALYSES
The cost of the survey, for all phases from the design through the report was
$44,061.79. Actual costs compared favorably with estimated costs except for coding
and getting the cards in shape for processing.
siderably underestimated.
Table 7.
The cost of this phase was con-
The actual costs, by phase of work, are shown in Table
Cost, by Item and Phase of Operation, for the Nashville Morbidity Survey
Item or Phase
Amount
Supplies (including printing Of questionnaires)
Direct Labor
1,952.;4
Sample design, selection and specification
Construction of questionnaire and preparation of interviewer's
manual
Hiring and training of interViewers
Interviewing
Interviewers
Supervision
Editing, coding and checking
Punching, verifying, and tabulating
Preparation of report
Travel
Communications
Total Direct Costs
Indirect Costs (at 15 percent of Direct Costs)
Total Cost
1,;72.67
1,999.37
1,928.76
7,4;0.66
5,490.58
8,528.38
3,531.62
640.72
5,01;.00
426.49
38,;14.59
5,747.19
44,061.78
7.
25
As a group, the interviewers employed on this survey were considered to
be more capable and efficient than these used by us on previous surveys.
Many
had considerable previous survey experience, yet maintained an open mind.
Al-
though our instructions and procedures were considerably more detailed and rigorous, than those they were accustomed to, they followed directions carefully.
Even so, there was still considerable variability in their performance or "production."
The major part of this was undoubtedly due to differences in their
inherent ability, but
worked.
may
be partly caused by the area of the city in which they
Table 8 indicates some of this variability.
The la.st two columns, hours
per completed schedule and the ratio of non-response (due to "no contacts and
refusals") to total possible schedules, might be considered roughly as a measure
of effectiveness.
This does
~
take into account the accuracy or completeness
of the responses or the amount of editing required.
This summary does include
the follow-up work on the "no-contacts" and the "respondent-failures" as well
as the regular assignments.
26
Table 8.
Summary of Interviewer Ferf'ormance
1
2
3
17
151
181
6
79
131
2
13
19
0
9
8
8
101.
158
20 8
1.9
1.4
u25
013
4
5
6
311
255
154
170
80
80
9
7
9
6
3
5
185
90
94
1.8
3.2
1.9
.05
..08
010
7
8
9
233
35
55
106
37
27
6
12
1
3
11
1
1:15
60
29
2 02
0.9
2.1
.05
.20
003
10
11
12
:153
160
188
87
85
88
32
10
7
9
IG8
le9
2.1
.25
11
128
106
106
13
14
15
292
182
219
201
96
131
13
34
17
a
15
248
97
163
1.5
1.9
1.7
.05
.01
.10
16
17
18
158
258
220
100
110
132
17
8
13
7
6
27
124
127
172
106
2",0
1.7
014
.06
.08
19
20
21
261
143
114
105
66
33
11
15
3
6
10
8
122
91
44
2,,5
2..2
3..4
009
.16
..07
22
23
24
390
143
105
206
63
57
22
11
12
34
26
5
262
100
74
1.9
2.3
1.8
.08
.11
.16
25
26
27
104
350
93
81
203
57
9
14
8
15
18
108
229
71
1.3
1.7
1.6
.08
.06
.11
* 28
* 29
38
23
20
12
2
3
7
7
29
22
·109
109
.07
010
4.t986
2,,649
306
308
3,,263
109
.09
*
Total
*
1
11
6
012
009
007
Supervisors who were assigned difficult cases or sampling units in undesirable
areas"
27
XII
SUMMARY
A sample of 3,032 sampling units having an expectation of 3, 060 sampling units
was drawn in NashVille, Tennessee and parts of its urban fringe to collect, by
personal interview, morbidity and mortality data from eligible households in the
area.
sample.
Interviews were obtained from 2649 of the 2974 eligible households in the
Interviewers were unable to contact 171 households and had refusals from
135 others to account for most of the non-response. A total of 282 SU's failed
to have any eligible households within them.
The interviewing was begun January 19, 1959 and wa.s completed by March 11,
1959. The field force consisted of two full-time supervisors, two part-time
superVisors and 29 interviewers.
In general, the qUality of the interviewing was
high.
Completed questionnaires were edited daily and mistakes or omissions were
returned to the interviewer immediately for correction or completion.
The edited
questionnaires were sent to North Carolina for coding and processing.
After the
data had been coded and placed on punched cards, a listing was made and checked
against the questionnaires to discover errors in coding or punching.
Corrected
decks were used in making the preliminary tabulations specified by the Air Pollution Medical Program, Public Health Service.
Seven decks composed of36;913 cards
were prepared.
Rela.tive sampling errors for a few selected items varied from 0.52 percent
for estimated total number of people in eligible households to 2.14 percent for
estimated total number of deaths occurring in eligible households during the past
five years.
As might be expected, in the estimation of proportions of households
exhibiting specified characteristics, the variance of the binomial is a good
approximation to the variance of the ratio estimate.
28
The total cost for the project was $44,061.78 including
costs and
~5,747.l9
for indirect costs.
~38,3l4.59
for direct
All cost items were estimated reasonably
well with the exception of the preparation of the data for processing.
This phaGe,
which includes the coding, punching, listing and checking operations, was considerably underestimated.
v
Appendix A..
Assignment of strata and sampling units to Planning Units
Planning
Unit
NOe
Number of
Dwelling
Units
12
13
886
999
2287
1331
17.31
2268
1605
11'71
1003
1~
1.
16
17
18
19
20
21
22
23
24
25
.26.
27,,28~29
30
31
32
33
35
34,,36
37
38
39
40
41
42
43
44
45:46
47
48
49
50
51
52
53
~~
56
57
65
66
67
73
74
Total
Number of
strata
3
10
7
51
64
20
31
20
62
56
84
42
10
4
24
20
23
12
32
35
39
42
25
1800
1170
1620
1215
1125
900
2925
2160
181.t5
1755
1845
1935
1710
675
135
450
315
2295
2880
900
1395
900
2790
2520
3780
1890
450
180
1080
900
1035
540
1440
1575
1755
1890
1125
1516
68,220
10015
22
50
29
38
,0
35
26
22
5
40
26
.36
27
25
20
65
48
1800
1208
1636
1223
1130
939
2916
2203
1863
1771
1861
1940
1730
684
152
487
340
2313
2921
938
1423
939
2791
2529
3782
1931
463
210
1080
934
1049
57$
69,224
SUs
IlExpected"
Size of SU
1.036
1.009
1.0l.6
1.020
1.012
1.008
1.OJ9
1.001
lc,013
100'(6
1.000
1.032
1.01.0
1.007
1.004
1.043
1.007
1.020
1.010
1.009
1.009
1.003
1.012
10013
1.126
1.082
1.079
1.008
10014
1.042
1.020
1.043
1.000
1.004
1.001
1.022
1,029
1.167
1.000
1.038
1.014
1.065
1.019
1.025
1 0 007
1.013
1.020
,
19
2i.~2
1~74
1768
1914
1148
N1JII1ber of
41
39
41
43
38
15
-
855
990
2250
1.305
1710
2250
1575
1J..70
990
22$