The statistics in this report are estimates derived from a sample. Two broad categories of error occur in such estimates: sampling and nonsampling errors. Sampling errors occur because observations are made only on samples of students, not entire populations. Nonsampling errors occur not only in sample surveys but also in complete censuses of entire populations. Nonsampling errors can be attributed to a number of sources: inability to obtain complete information about all students in all institutions in the sample (some students or institutions refused to participate, or students participated but answered only certain items); ambiguous definitions; differences in interpreting questions; inability or unwillingness to give correct information; mistakes in recording or coding data; and other errors of collecting, processing, sampling, and imputing missing data.

Weighted item response rates were calculated for all variables used in this report. The weighted item response rate was calculated by dividing the weighted number of valid responses by the weighted population for which the item was applicable. Overall, most of the items had very high response rates. Three variables had weighted item response rates below 85 percent. In two of these cases (the reason the respondent did not consider the current job the start of a career [CECURJOB] and whether the respondent had received unemployment compensation since last working [CEUNEMPL]), the low weighted response rate is due largely to the fact that the variables were applicable to a small proportion of the sample. That is, because applicability could not be determined for respondents with incomplete interviews, those respondents are considered to have indeterminate responses. Incomplete interviews thus make up a relatively high proportion of the indeterminate responses for those items. However, it is highly likely that the majority of incomplete interviews would have been excluded from the item had their information been gathered. When incomplete interviews are excluded from the calculation of the item response rates, the response rates for CECURJOB and CEUNEMPL are 97.5 and 98.7 percent, respectively.

For the remaining variable (grade-point average in undergraduate major [GPAMAJ]), an analysis of item nonrespondents was conducted. Item respondents were compared to item nonrespondents on the following variables: percent female (GENDER); percent White, percent Black, percent Hispanic, and percent Asian (RACE2); percent enrolled full time, part time, or not enrolled as of 2001 (ENRCUR); percent working full time, part time, or out of the labor force as of 2001 (EMPOLF); percent majoring in various fields (BMAJORS3); and cumulative GPA (GPA2). The results suggest that, compared with those who responded to the item GPAMAJ, nonrespondents were less likely to be White and more likely to be Hispanic; were less likely to be enrolled full time in school in 2001 and more likely to be not enrolled; were less likely to be employed part time in 2001; were less likely to have majored in physical sciences or vocational fields and more likely to have majored in another unspecified major; and had lower overall GPAs. Therefore, nonrespondents to the item GPAMAJ are likely to have had lower major GPAs as well. This bias is likely to have depressed any relationships between GPAMAJ and other variables; that is, the relationships between GPAMAJ and other variables discussed in this report are likely to be underestimated.