- 4 -

Technical Note

   The estimates in this release were obtained using data from
the first 22 rounds of the National Longitudinal Survey of Youth
1979 (NLSY79).  This survey is conducted by the Center for Human
Resource Research at The Ohio State University and the National
Opinion Research Center at the University of Chicago under the
direction and sponsorship of the U.S. Department of Labor’s
Bureau of Labor Statistics.

Sample

   The NLSY79 is a nationally representative sample of 12,686
young men and women who were 14 to 22 years of age when first
surveyed in 1979.  This survey sample was initially composed of
three subsamples:
     
  --A cross-sectional sample of 6,111 youths that was designed
    to represent the noninstitutionalized, civilian population of
    young people living in the U.S. in 1979 and born between January 1,
    1957, and December 31, 1964.
     
  --A supplemental sample of 5,295 youths designed to oversample
    noninstitutionalized, civilian black, Hispanic or Latino, and
    economically disadvantaged nonblack, non-Hispanic youths living
    in the U.S. in 1979 and born between January 1, 1957, and December 31,
    1964.

  --A military sample of 1,280 youths born between January 1, 1957,
    and December 31, 1961, and enlisted in the Army, Air Force, Navy, or
    Marine Corps as of September 30, 1978.
     
   In 1985, the military sample was discontinued, and, in 1991,
the economically disadvantaged nonblack, non-Hispanic youths were
dropped from the supplemental sample.  As a result, the NLSY79
sample now includes 9,964 individuals from the cross-sectional
sample and the black and Hispanic or Latino supplemental samples.
(This sample size is not adjusted for sample members who have
died.)

   Individuals were surveyed annually from 1979 to 1994 and
biennially since 1994.  In 2006-07, 7,654 individuals responded
to the survey, for a retention rate of 77 percent.  Only these
individuals are included in the estimates in this release.  All
results are weighted using the 2006-07 survey weights that
correct for the oversampling, interview nonresponse, and
permanent attrition from the survey.  When weighted, the
estimates represent all persons born in the years 1957 to 1964
and living in the U.S. when the survey began in 1979.  Not
represented by the survey are U.S. immigrants who were born from
1957 to 1964 and moved to the United States after 1979.
     

                                   - 5 -

Work history data

   The total number of jobs that people hold during their work
life is an easy concept to understand but a difficult one to
measure.  Reliable estimates require a survey that interviews the
same people over the course of their entire work life and also
keeps track of all the jobs they ever held.  The NLSY79 tracks
the number of jobs that people have held, but the respondents in
this survey are still relatively young, ages 41 to 50 in 2006-07,
and have many years of work life ahead of them.  As the cohort
continues to age, however, more complete information will become
available.
   A unique feature of the NLSY79 is that it collects the
beginning and ending dates of all jobs held by a respondent so
that a longitudinal history can be constructed of each
respondent’s work experiences.  The NLSY79 work history data
provide a week-by-week work record of each respondent from January
1, 1978, through the most recent survey date.  These data contain
information on the respondent’s labor force status each week, the
usual hours worked per week at all jobs, and earnings for all
jobs.  If a respondent worked at more than one job in any week,
hours and earnings are obtained for additional jobs.  When a
respondent who missed one or more consecutive survey rounds is
interviewed again, he is asked to provide information about all
time since the last interview.
     
Interaction between time and age in a longitudinal survey

   Because the NLSY79 is a longitudinal survey, meaning the
same people are surveyed over time, the ages of the respondents
change with each survey round.  It is important to keep in mind
this inherent link between the calendar years and the ages of the
respondents.  For example, table 5 reports earnings growth from
age 23 to age 27.  The youngest respondents in the sample (birth
year 1964) were these ages during 1987-91, whereas the oldest
respondents (birth year 1957) were these ages during 1980-84.

   Although participants in the NLSY79 were ages 41 to 50
during the 2006-07 interviews, this release covers only the
period while the respondents were ages 18 to 42.  The reason for
not including older ages is that the sample sizes were still too
small to provide statistically reliable estimates for age groups
older than 42.  As the NLSY79 continues to be administered and
the respondents age, subsequent rounds of the survey will enable
analyses to be conducted for older age groups.

   As with age, the educational attainment of individuals may
change from year to year.  In the tables and analysis presented
in this report, educational attainment is defined as of the 2006-
07 survey.  This definition is used even when data on age and
educational attainment are presented together.  For example,
table 1 reports the number of jobs held during different age
categories.  Suppose that a respondent had completed a bachelor’s
degree at age 28.  That respondent would be included in the
"Bachelor’s degree and higher" educational category in all age
categories shown on the table, even though he or she did not have
a bachelor’s degree at any point from age 18 to age 27.


                                   - 6 -

Definitions

   Job.  A job is defined as an uninterrupted period of work with a
particular employer.  Jobs are therefore employer-based, not
position-based.  If a respondent indicates that he or she left a
job but in a subsequent survey returned to the same job, it is
counted as a new job.  For example, if an individual worked in a
retail establishment during the summer, quit at the end of summer
to return to school, and then resumed working for the same
employer the following spring, this sequence would count as two
jobs, rather than one.  For self-employed workers, each "new" job
is defined by the individuals themselves.

   Unemployment.  If respondents indicate a gap between employers,
they are asked how many of those weeks they spent searching for
employment or on layoff.  For that number of weeks, they are
considered unemployed.  For the remaining weeks, they are coded
as not in the labor force.  No probing for intensity of job
search is done.

   Usual earnings.  Respondents can report earnings over any time
frame (hour, day, week, month, year).  For those who do not
report an hourly wage, one is constructed using usual hours
worked over that time frame.  Wages greater than $100 per hour
and less than $1 per hour were not included in the analysis of
earnings growth because the reported earnings levels were almost
certainly in error.  For the same reason, individuals who had
inflation-adjusted earnings growth greater than 100 percent were
not included in the analysis.  These exclusions from the analysis
affected 82 respondents.

   Race and ethnicity groups.  In this release, the findings are
reported for non-Hispanic whites, non-Hispanic blacks, and
Hispanics or Latinos.  These three groups are mutually exclusive
but not exhaustive.  Other race groups, which are included in the
overall totals, are not shown separately because their
representation in the survey sample is not sufficiently large to
provide statistically reliable estimates.  In other BLS
publications, estimates usually are published for whites, blacks,
and Hispanics or Latinos, but these groups are not mutually
exclusive.  The terms "Hispanic or Latino" are considered to be
an ethnicity group, and Hispanics or Latinos can be of any race.
Most other BLS publications include Hispanics or Latinos in the
white and black race groups in addition to the Hispanic or Latino
ethnicity group.

   Information in this release will be made available to sensory 
impaired individuals upon request.  Voice phone:  (202) 691-5200; 
TDD message referral phone:  1-800-877-8339.