March 3, 2002

Getting Serious Online: As Americans Gain Experience, They Pursue More Serious Activities

Methodology

This report is based on the findings of two surveys; a daily tracking survey on Americans’ use of the Internet conducted March 1-31, 2000, and a callback survey conducted among the same group March 12 to April 9, 2001. Results are based on data from telephone interviews conducted by Princeton Survey Research Associates. Data is based on 1,501 cases where complete interviews were conducted in both 2000 and 2001. For results based on the total sample, one can say with 95% confidence that the error attributable to sampling is plus or minus 3 percentage points.  For results based Internet users, the margin of sampling error is plus or minus 4 percentage points.  In addition to sampling error, question wording and practical difficulties in conducting telephone surveys may introduce some error or bias into the findings of opinion polls.

The original sample used for the March 2000 survey is a random digit sample of telephone numbers selected from telephone exchanges in the continental United States. The random digit aspect of the sample is used to avoid “listing” bias and provides representation of both listed and unlisted numbers (including not-yet-listed numbers). The design of the sample achieves this representation by random generation of the last two digits of telephone numbers selected on the basis of their area code, telephone exchange, and bank number.

New sample was released daily and was kept in the field for at least five days. This ensures that complete call procedures were followed for the entire sample. Additionally, the sample was released in replicates to make sure that the telephone numbers called are distributed appropriately across regions of the country. At least 10 attempts were made to complete an interview at every household in the sample. The calls were staggered over times of day and days of the week to maximize the chances of making contact with a potential respondent. Interview refusals were recontacted at least once in order to try again to complete an interview.  All interviews completed on any given day were considered to be the final sample for that day.  Follow-up interviews were attempted with all 3,533 respondents who completed an interview in March 2000.  Successful March 2001 interviews were conducted with 1,501 (42%) of the original respondents.

Non-response in telephone interviews produces some known biases in survey-derived estimates because participation tends to vary for different subgroups of the population, and these subgroups are likely to vary also on questions of substantive interest. In order to compensate for these known biases, the sample data are weighted in analysis. The demographic weighting parameters are derived from a special analysis of the most recently available Census Bureau’s Current Population Survey (March 2000). This analysis produces population parameters for the demographic characteristics of adults age 18 or older, living in households that contain a telephone. These parameters are then compared with the sample characteristics to construct sample weights. The weights are derived using an iterative technique that simultaneously balances the distribution of all weighting parameters.