foreign countries.
Starting with a national sample of approximately 4,800 U.S.
households in 1968, the PSID has traced individuals from those
households since that time, whether or not they are living in the
same dwelling or with the same people. Adults have been followed
as they have grown older, and children have been observed as they
advance through childhood and into adulthood, forming families of
their own. Each year information is collected about the PSID's
sample members (members of the PSID's 1968 sample families or
their offspring) and their current co-residents (spouses,cohabitors,
children, and others living with them), even if those co-residents
were not part of original-sample families.
Because the original focus of the study was on the dynamics of
poverty, the 1968 sample included a disproportionately large
number of low-income households. The oversampling of families
poor in the late 1960s resulted in a sizable sub-sample of blacks.
Probability-of-selection weights enable analysts to make estimates
from the sample that are representative of the U.S. population. In
the absence of nonresponse bias, the PSID's rules for tracking
individuals and families over time lead to accurate representation of
the nonimmigrant U.S. population both cross-sectionally each year,
and in terms of change, since 1968. To help correct for omissions in
representing post-1968 immigrants, a representative sample of
2,043 Latino (Mexican, Cuban, and Puerto Rican) households was
added in 1990.
The study's tracking rules, along with its Latino subsample
addition in 1990, have meant substantial increases in the number
of individuals in the study as it has progressed through time. In
1968 the PSID gathered information about approximately 18,000
individuals; by 1988 this number had grown to a cumulative total of
about 37,500. Similarly, the number of family units has increased
from just under 5,000 at the beginning of the study to about 7,000
currently, not including Latino households.
The PSID provides a wide variety of information at the family
and individual level, as well as some information about the locations
in which sample households reside. The central focus of the data
is economic and demographic, with substantial detail on income
sources and amounts, employment, family composition changes,
and residential location. Content of a more sociological or
psychological nature is also included in some waves of the study.