Methodology

Results for the survey are based on telephone interviews conducted under the direction of Princeton Survey Research Associates among a nationwide sample of 2,528 adults, 18 years of age or older, during the period July 14 – August 5, 2003. Based on the total sample, one can say with 95% confidence that the error attributable to sampling and other random effects is plus or minus 2 percentage points. For results based on either Form 1 (N=1,284) or Form 2 (N=1,244), the sampling error is plus or minus 3.5 percentage points. For results based on registered voters (N=1,866) the sampling error is plus or minus 2.5 percentage points.

Respondents who indicated they would prefer to complete the interview in Spanish, plus Spanish-speaking households in which no eligible English-speaking adult was available, were contacted by a Spanish-speaking interviewer. A total of 56 interviews were conducted in Spanish.

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 one 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 10 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.

The demographic weighting parameters are derived from a special analysis of the most recently available Census Bureau’s Current Population Survey (March 2002). This analysis produced population parameters for the demographic characteristics of households with adults 18 or older, which are 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.

About the Values Project

The values project draws on a series of large national surveys conducted since 1987. The project was initiated by the Times Mirror Center for the People and the Press in 1987 and continued by the Pew Research Center for the People and the Press since 1996. Over this period, 12 surveys have been conducted with a total of 27,550 interviews. Interviews included approximately 80 questions about political and social values, plus questions about current issues and political figures.

Sample Margin Interview

About the Party Identification Database

The analysis of change in the public’s identification with the two major parties is based on a compilation of Pew Research Center surveys from January 1997 to October 2003. These surveys were combined into one large data file that could be sorted according to a range of demographic characteristics, with comparisons made across different time periods. The table below shows the number of interviews for the total database and for time periods referred to in the report.

Details about the Value Scales

To provide a summary measure of each topic area covered by the values questions, several items were combined using a technique called “factor analysis.” This statistical procedure combines measures that are capturing a common concept (e.g., commitment to religion), giving each measure a different weight according to how similar it is to the concept being measured. Each person in the survey is then assigned a score on the scale, and these scores can be compared over time or across groups (for example, between Democrats and Republicans).

The survey items in each scale are listed below, along with the percentage who agreed or disagreed with each one in 2003.