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Attrition and the

National Longitudinal

Surveys of Labor
Market Experience:

Avoidance, Control

and Correction

by Dr. Patricia Rhoton'

Data Archivist

Center for Human Resource Research

The Ohio State University

Since 1966 the Center for Human Resource

Research has been analysing the longitudinal

surveys conducted by the Census Bureau for the

Department of Labor. The main purpose of

'This report was prepared under a contract with
the Employment and Training Administration,
U.S. Department of Labor, under the authority
of the Comprehensive Employment and Training
AcL Researchers undertaking such projects
under government sponsorship are encouraged to

express their own judgments. Interpretadons or
viewpoints stated in this report do not
necessarily represent the ofiicial position or
policy of the U.S. Department of Labor.

these surveys is to study the labor force activity

of different population groups. The original

groups included men who were 45-59 years old

in 1966, women who were 30-44 years old in

1967, men who were 14-24 years old in 1966,

and women who were 14-24 years old in 1968.

In 1979, a new survey, conducted by the

National Opinion Research Center {editor's

note:) (NORC) in Chicago, was added for young

men and women who were 14-21 in that year.

Each of the five surveys is designed to collect

information on all phases of the respondent's

labor force activity and on other characteristics

such as educational attaiiunent, health, family

composition, and financial status that are known
to be related to such activity.

The original plan in 1965 was to interview the

same respondents each year for a period of five

years. Because of the usefulness of the data

and the relatively small sample attrition, a

decision was made at the end of the first

five-year period to continue for another five

years. The interview pattern was changed at

that time from a face to-face yearly interview

to a 2-2-1 pattern. Each respondent was

contacted by phone every two years, then again

in person one year after the second phone

interview. This pattern was used again both

during the third five-year extension obtained in

1976 and during the fourth five-year extension,

obtained in December 1982. At the time of the

most recent extension, a study looking

specifically at attrition within the different

cohorts was carried ouL

Longitudinal studies in general have several

advantages over the more frequent

cross-sectional studies. While longitudinal

studies are very expensive, the data are collected

in great detail over time, with respondents

reporting events and attitudes as they occur

rather than retrospectively. Collecting the data

in this way also enables the researcher to go

beyond issues of correlations to address the

more urgent issues of causalit>'. The main

advantage of a longitudinal survey, following the

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same set of respondents year after year, aeates

two major problems, however. The first is the

difRciilty of relocating respondents for

subsequent interviews, and the second is

maintaining respondent cooperation over

repeated interviews.

Attrition in the NLS

Table P shows the numbers and percentages of

respondents for all interviews up to and

including the 1983 questionnaire. The base year

row shows only those respondents who were

interviewed that first year. Between the original

SCTeening and the first interview, some of the

eligible respondents were lost: 9.0 percent of the

Older Men, 5.5 percent of the Older Women,
8.3 percent of the Young Men, 5.8 percent of

the Young Women, and 11.5 percent of the

New Youth.

While Table 1 shows the distribution of

interviews between and among the five cohorts.

Tables 2-5 show interview/noninterview status

of the four older cohorts by reason for

noninterview. While there are difTerences

between the cohorts in the distribution of

reason for noninterview, within each cohort the

distribution of reason remains consistent across

the years. The method of interview, whether

face-to-face or by telephone, does not seem to

affect the attrition rate. Some of the losses in

the sample are unavoidable. In the Survey of

Mature Men (Table 2), for example, an

increasing percentage of sample losses are due

to respondent deaths. The Mature Women's
survey (Table 3) has the second highest

retention rate among the four older cohorts.

This high rate is probably due to the fact that

this group is very stable and has low geographic

^Editor's note: Tables are gathered together at

end of article

mobility.

The Young Men's cohort has the lowest rate of

retention and has been the test case for new
attempts to stop the gradual decline in sample

size. A variety of factors account for the

difficulty in locating these respondents:

completion of school, acquisition of new jobs,

formation of families, and movement in and out

of the military services. The higher rates of

attrition in the earUer years were attributed to

influx into the mihtary since the sample was

drawn, and initial interviewing done during the

Vietnam War. However, rates remained high

even as these respondents returned from the

military.

The Yoimg Women's cohort, which is similar to

the Young Men's with respect to completion of

school, acquisition of new jobs, and formation

of families, posed the added challenge of name
changes accompanying changes in marital status,

yet the overall response rate has remained high.

The New Youth cohort has benefited greatly

from the lessons taught by experience with the

four older cohorts. In 1983, the response rate

for this group was 96.3 percent A comparison

between this cohort and the first five years of

the Young Women's cohort, which had the best

retention rate of the older cohorts, shows that

different procedures and techniques can

substantially decrease attrition.

Not only does NORC have a higher overall

interview rate, but also the organization seems

to be better at retrieving respondents. In 1982,

96.0 percent of the original 1979 sample were

interviewed. Some of these had not been

interviewed in previous years: 2.2 percent in

1980, 1.1 percent in 1981, and 0.5 percent in

1980 or 1981. Only 165 respondents (one

percent) of the original sample had had only

one interview after four roimds of the survey.

In 1983, the number of respondents who had

had only one interview dropped to 115. Over

eleven thousand (90.7) respondents had been

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interviewed every year, and 5.5 percent had

completed four out of the five interviews.

The Impact of Attrition od Representativeness

The gradual decline in sample size over time

becomes very important if it results in a biased

sample. While each cohort was checked at the

end of the first five-year series of interviews,

and smaller checks were made in the context of

reports on occupational distribution, educational

attainment, age distributions, and marital status

with published national data, no one looked at

all the cohorts systematically until 1982. At this

point the issue of representativeness had to be

addressed as part of the proposal to extend the

cohorts for another five years.

Such a study could essentially be carried out in

either of two ways. First, the remaining sample

could be compared with some outside group,

such as the decennial Census or the Current

Population Survey. Comparison with an outside

sample was difficult given time constraints and

the fact that Census data were not yet ready for

release. While the CPS data were available,

differences between the CPS and each of the

four older cohorts had already been documented

in the first year. The second alternative was to

compare the characteristics of the respondents

who were left after ten years with the

characteristics of all respondents interviewed in

the initial year to see how much difference, if

any, there actually was. Each cohort was

checked for differences in the age distributions,

educational attainment levels, employment status,

industry and occupation distributions, marital

status, SMSA status, annual income distribution,

and wage and salary' distribution. The Yoimg
Men and Young Women were also checked for

differences in enrollment status.

A separate evaluation was done by race for

each of the four cohorts. Table 6 is an

example of the type of table constructed for

each group. The ten-year sample was weighted

using two methods: the entry level weight and a

ten-year weight, which includes successive

adjustments for each year's noninterviews. For

aU cohorts except the Young Men, the relevant

comparison was between the entry year

weighted figures and the ten-year sample using

the ten-year weight In the Young Men's

cohort, the 1966 sample using the 1966 weight

was compared to the 1976 sample using the

1966 weight because the 1976 weight had been

adjusted to include individuals formerly in the

military. Since young men already in the

mihtary had been deliberately excluded from

the Young Men's sample, using the 1976 weight

could have created apparent differences where

none existed. For this group alone, it was more
appropriate to use the 1966 weight

Table 7 summarizes the distribution of

differences by cohort and shows that for most

characteristics the difference between the two

samples was less than two percentage points.

After the differences were identified, statistical

tests of significance were computed for each of

the comparisons. Table 8 shows the number of

statistically significant differences at various

levels for each cohort by race. While the

number of differences was higher than would

be expected by chance, several were based upon

small sample cases in the initial year and

characteristics with only two values. In the

latter cases, a statistically significant result in

one category means the other category will also

be statistically different [sic].

After reviewing the entire set of tables, it was

clear that noninterviews had not seriously

distorted the representativeness of the sample.

Given this finding, and the ability to apply

weights to eliminate any potential bias, the

decision was made to continue all four surveys

for another five years.

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26 - iassist quarterly

It is unclear, however, how further erosion of

the samples will affect representativeness.

Concern with this issue, together with the

higher noninterview rates that NORC was

having with the New Youth sample, led to an

evaluation of the rules that had been established

in the original five-year period and an attempt

to see if it was possible to retrieve some of the

noninterview cases.

Retrieving Former Noninterview Cases

Since the Yoimg Men's panel had lost the most

respondents, it became the target for the first

attempt at retrieval. Respondents from the

1975, 1976, 1978 and 1980 survey years, who
normally would not have been included in the

workload (i.e., attempted contacts) because of

noninterview status in those years (refused,

unable to contact, institutionalized, moved
outside the U.S.) were sorted, and a sample of

279 selected.

Several changes were made in the procediu^es

for contacting these special respondents. No
restrictions were placed on the number of

telephone calls, mileage, or time spent locating

and retrieving these respondents. Each

interviewing packet included the respondent's

most recently completed interview and

household record card, as well as the most

recent questionnaire, and all record cards for

any other household members participating in

any of the other cohorts. In addition, an

expanded list of methods of locating respondents

was included. As a result of these additional

steps, 104 (37.3 percent) of these respondents

were interviewed. These interviews have been

flagged and will be checked as soon as the data

tapes are available from the Census Bureau to

determine if they differ in any way from the

rest of the respondents. If these respondents

remain in the sample for the next round of

interviews in the latter part of 1983. a concerted

effort may be made to use these procedures

during the regular interviews and in similar

attempts to retrieve noninterviews in the other

three cohorts.

Differences Between Census and NORC

One of the major differences between Census

and NORC is the amount of location

information obtained from the respondent

NORC obtains more information, and request

information on other individuals with specific

relationships to the respondent, depending upon
the respondent's circumstances. The interviewer

begins by asking the name, relationship, address,

and phone number of the person most likely to

know where the respondent is. If the

respondent is Uving in a dormitory, fraternity,

sorority, hospital or other temporary situation,

the interviewer is instructed to obtain the name
and relationship of a householder at a

permanent home address. If the respondent is

married and living apcirl from a spouse, the

spouse's address and telephone nimiber are

requested. If the respondent is not living with

a parent and has not provided a parent's name,

this information is obtained, including whether

or not the parents live together. The name of

another relative with whom the respondent is in

contact, and the names of friends and places to

which the respondent goes when not spending

spare time at home, are also obtained.

Respondents are also asked for nicknames,

maiden names if they are married women, and

whether or not they expect to move in the next

12 months.

This extensive list gives the NORC interviewer

a real advantage when contacting someone on

the list, since the ability to mention the

respondent's parents, relatives, friends, hangouts

or nicknames demonstrates that the interviewer

Summer 1986



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knows the respondent to some degree and may
make the reference more willing to give out

information about the respondenL Another

major advantage that the NORC interviewer has

over the Census interviewer is the existence of

a centralized locating shop in Chicago. The

person working at the locating shop has access

to all previous questionnaires, original copies of

locator documents and information about the

respondent's brothers and sisters. Working with

this additional data, the respondent can usually

be located by phone and reassigned to the same

or another interviewer. The Census interviewer

starts out with less information with which to

locate the respondent. S/he has a questionnaire

with a label indicating the respondent's name
and most recent home address. In addition,

there is a household record card for each

respondent which contains the telephone

numbers, all addresses at which the respondent

has lived since the survey began, the names of

all persons who have lived with the respondent,

and the names, addresses and telephone

numbers of only two persons who will always

know where s/he can be reached.

Besides the more extensive locating supplement

that NORC builds in the interview, several

other differences appear. Each respondent in

the New Youth cohort is paid $10.00 for a

completed interview, since many researchers

believe that even a small amount of money
helps in obtaining cooperation, especially among
younger respondents. The New Youth

respondents also had an opportunity' to take a

series of tests for the Department of Defence,

which needed to evaluate tests given to

individuals in the military. For these tests,

which take several hours, the respondents were

paid $50.00. When the four older cohorts were

first interviewed, paying respondents was not as

well accepted. Now there are fears that starting

this procedure with the older cohorts would

cause concern on the part of respondents.

they will be interviewed each year for the next

several years and are therefore aware that they

will be contacted about the same time each

year. The Census interviewers are told only

that they may be conducting additional surveys,

and should not tell the respondents that this is

the last time s/he will be interviewed. The lack

of an answer to give the respondent, in addition

to the 2-2-1 pattern, probably leaves the

respondent without a sense of when or if s/he

will be contacted again. While this ambiguity

may not have an impact on their cooperation in

the survey, the NORC approach leaves the

respondent with a greater feeling of certainty

about the interviewing schedule.

Revising the Rule for Dropping Respondents

After the first year, respondents in the four

older cohorts who refused to participate or had

died, were dropped from the Census sample.

Those who were not reinterviewed for any

reason for two consecutive years were also

dropped. The only exception was made in the

Young Men's sample with those respondents

who were in the Armed Forces. Since the

sample was to represent the national civilian,

non-institutionalized population, young men
were not interviewed while they were in the

Armed Forces but were retained in the sample

and reinterviewed in the first interview after

they had left the services. However, NORC's
success in retrieving respondents even after they

had refused and the success of the Young Men
retrieval effort resulted in a change in these

rules. Cunently, no respondent is dropped

except those who have died. NORC goes back

each year and attempts to interview all living

respondents.

Another procedural difference is that New
Youth cohort respondents are told up front that

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Maintaining Respondent Cooperation Conclusions

While both Census and NORC send out

advance letters about the entire survey, stressing

the importance of the respondent's cooperation,

NORC also sends out a newsletter that tells

respondents in a very "chatty" format about

some general results of the previous survey.

The Census Bureau had a short, formal fact

sheet that went out with the cover letter, but

interviewers reported that respondents did not

feel it was very useful. In the 1982 Young
Women's survey, a more extensive description of

the surveys and a list of the research results

from the survey were sent to any respondent

who filled in and returned a postcard requesting

additional informatioa Over one-third of the

respondents interviewed in that wave mailed in

the postcard. A variable will be created

identifying these respondents and if distribution

of the handbook inaeases the response rate in

the next round, the handbook will be offered to

the respondents in all three cohorts.

The New Youth survey has, at this time, a

considerably better response rate than any of

the four older cohorts. Much of its success can

be traced to the solution of problems that

developed over time in the fouj older cohorts.

While the necessity of maintaining the same
measures over time prevented change in the

handhng of the four older cohorts, these

problems were conected in the first wave of the

New Youth cohort Questions that the

respondents or the interviewer had difficulty

with in the four older cohorts were altered so

that there was no confusion from the very

beginning. Perhaps most importantly, given the

highly mobile nature of the younger age group,

much more detail was obtained on individuals

who would always know where the respondent

was. In addition, more information about the

survey was given to the respondent before,

during and after each interview. All these

factors combined have resulted in a response

rate that is very good for any survey and

exceptional for a longitudinal survey in its fifth

year, n

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Table 1

M

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Table 2

c —

32-

£-

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Table 3

£.:

1. Ni?

&,

»± I

II.

£ a— £

o

tl

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Table 4

• ^1

e-s

§o

II

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iassist quarterly - 33

Table 5

s §

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Table 6

Table 6 Selected DiBracterisli in 19r.6 of Original Srnple and Simple Inlerviewd in 1976

Milurc W-n - Mii tcs Only

Qinracleristics Nirrt>or of

In 1966 respondcnij
in 1566

« potcntiiil ly

el ipible for

laCfi sn. |ile

l\c I Killed

m 1 ng

UnweiRhled 19611 weiRlit'

« % (I %
(nop)

Unweighted 19G6 wc

« % I

(OOP)

ARe
45-49 1329 1202 39.3
50-54 1230 1043 34.1

55-59 1041 811 26.5
Educational
Btlairment
Less then U yrs. 2038 1679 55.3
12 years 885 778 25.fi

Nbre than IJ yrs. 655 583 19.2
Ehplo^Tnent stat

Fhployed 3348 2897 94.9
Unsiployed 46 38 1 .2

Out of labor force 206 121 4.0
Industry'
A^r iculturc 335 293 10.1
Mining 30 25 .9

Construction 351 292 IP.l

^Vlnu^6Ctu^lnK 1000 866 29.9
Transporlatlon 315 2f.3 9.1

Public adnin.

hVirltal status

Never morrled

Occupation^
Professional 359

NV\nager lal 582

Clerical 173

Sales 176

Crafts 828

Operatives 572
Household -

Services 180
Fanwrs 255
Farm laborers 60

Laborers 154

S^CA status
In SMSA 2487

Out of SNEA 1112

Annual Incone

fqual to lero 5

1-2,199 249
3,000-9,999 1418
10,000-14,999 712
15,000-19,999 211
* 20,000 156

Wages and salary
E<5ubI to zero 777

1-2,999 243
3,000-9,999 1690

10,000-14,999 447

15,000-19,999 81

• 20,000 60

'Excludes death, nnilitarv end

^hose orployed sijrvey week.

80.3
81.2
82.6

82.6
90.4
92.0
82.4

71 .1

91 .0

flfi.O

1329

1230
1041

36.9 4996 36.5

57.0 7645
24.7 3385
18.3 2561

39.0 3691

34.4 3239
26.6 2610

652 25.9 2486 26.1

335 10.0 1171 9.2
30 0.9 lie 0.9

351 10.5 1335 10.5
loop 29.9 3805 30.0
315 9.4 1213 9.6

12.9 1644

90.1

5.3

4.6

12278

732
624

90.0
5.4

4.6

10.8 1406 11.1

17.4
5.2

5.3

2245
667

688

17.7

5.3

5.4

24.8 3153 24.9

17.1 2198 17.3

25.9 2765

777 23.5 2876 23.0

1834 19.3

4482 38.8

3917 33.9

3152 27.3

6294 54.6
3002 26.1

2222 19.3

3348 93.0 12709 93.0 2395 95.0

10.2 IlPO 10.

P

702 29.3 2660 29.4

375 15.7 1441 15.9

1094 10.0

3220 29.4

1036 9.5

1746 15.9

12.6 1142 12.6 1388 12.7

2298 91.3 8695 91 .3 10526 91.3

10.6 999 11.1 1218

17 7 1623 18.0 1969

4.9 446 5.0 542

5.2 491 5.4 597

24.9 2249 24.9 2722

16.7 1544 17.1 1867

22.3 20P9 21.9 2420 21.

B

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Table 7

Table 8

Table 7 Nintoer and Percentage of Differences by Panel

~~ ~
Absolute differences C^)

Panel 0^ 2^3 3+ Total

Mature men
Black 34 (73.9 8 (17.4) 4 (8.7) 46 (100.0)

White 43 (95.6) 2 (4.4) 45 (100.0)

Mature wcmen
Black
Mii tp

Young men
Black 30 (73.2) 5 (12.2) 6 (14.6) 41 (100.0)

White 43 (97.7) 1 (2.3) 44 (100.0)

Young wonen
Black 33 (82.5) 6 (15.0) 1 (2.5) 40 (100.0)

White 40 (95.2) 2. (4.8) 42 (100.0)

42 (93.3) 3 (6.7) 45 (100.0)

45 (100.0) 45 (100.0)

Table 8 Nurber and Percentage of Statistically Significant Differences by
Panel

Level of significance
Panel 190 2% 3%

Mature men
Black 4 (9.1) 7 (15.9) 12 (27.3)
^>iite 4 (9.1) 7 (15.9) 14 (31.8)

Mature women
Black 2 (4.5) 2 (4.5) 3 (6.8)
White 1 (2.3) 4 (9.3) 5 (11.6)

Young Men
Black 1 (2.6) 4 (10.3) 6 (15.4)
VN'hitc 2 (4.7) 4 (9.3) 6 (14.0)

Young wonen
Black 1 (2.6) 3 (7.9) 4 (10.5)
V-liite 1 (2.6) 2 (5.1) 2 (5.1)

Summer 1986