Results for this survey report are based on telephone interviews conducted under the direction of Princeton Survey Research Associates among a nationwide sample of 3,184 adults, 18 years of age or older, during the period October 26 to December 1, 1998. The technology survey included interviews with a national sample of all adults, and an additional oversample of 1,184 adults who use the Internet. Several results were also drawn from a survey of a nationwide sample of 1,201 adults conducted December 9-13, 1998.
[N = 2,000]
In addition to sampling error, one should bear in mind that question wording and practical difficulties in conducting surveys can introduce error or bias into the findings of opinion polls.
Survey Methodology in Detail
The sample for this 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). The design of the sample ensures 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.
The telephone exchanges were selected with probabilities proportional to their size. The first eight digits of the sampled telephone numbers (area code, telephone exchange, bank number) were selected to be proportionally stratified by county and by telephone exchange within county. That is, the number of telephone numbers randomly sampled from within a given county is proportional to that county’s share of telephone numbers in the U.S. Only working banks of telephone numbers are selected. A working bank is defined as 100 contiguous telephone numbers containing three or more residential listings.
The sample was released for interviewing in replicates. Using replicates to control the release of sample to the field ensures that the complete call procedures are followed for the entire sample. The use of replicates also insures that the regional distribution of numbers called is appropriate. Again, this works to increase the representativeness of the sample. At least five attempts were made to complete an interview at every sampled telephone number. The calls were staggered over times of day and days of the week to maximize the chances of making a contact with a potential respondent. All interview breakoffs and refusals were re-contacted at least once in order to attempt to convert them to completed interviews. In each contacted household, interviewers asked to speak with the “youngest male 18 or older who is at home.” If there is no eligible man at home, interviewers asked to speak with “the oldest woman 18 or older who is at home.” This systematic respondent selection technique has been shown empirically to produce samples that closely mirror the population in terms of age and gender.
Non-response in telephone interview surveys 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.
Weighting for the General Public Sample
The demographic weighting parameters are derived from a special analysis of the most recently available Census Bureau’s Current Population Survey (March 1996). This analysis produced population parameters for the demographic characteristics of households with adults 18 or older, which were then compared with the sample characteristics to construct sample weights. The analysis only included households in the continental United States that contain a telephone. The weights are derived using an iterative technique that simultaneously balances the distributions of all weighting parameters.
Weighting for the Internet Users Sample
The demographic weighting parameters for the sample of Internet users were derived by averaging the estimates of the demographic distribution of Internet users across four weighted national samples of all adults. Those samples came from the general public component of this survey, and from three other national surveys conducted in August and September. This analysis produced estimates of population parameters for the demographic characteristics of adult Internet users, 18 or older, which were then compared with the sample characteristics to construct sample weights. The weights are derived using an iterative technique that simultaneously balances the distributions of all weighting parameters.
