Conclusion

It seems appropriate to close this report of the 1996 Phi Delta Kappa/Gallup Poll of the Public's Attitudes Toward the Public Schools with some thoughts about the collective responsibility we all have for communicating with the public. The public is largely dependent on the mass media for information about the public schools. If people are not well informed, it seems likely that media gatekeepers are not functioning as well as they might. This puts an added burden on public school leaders, for their responsibility for communicating complete and accurate information to the public becomes heavier. If the information the public receives is accurate, comprehensive, and balanced, people are in a position to do what people are supposed to do in a democracy: decide what the future of the public schools will be.

Methodology

Research Procedure

The Report

Due allowance must be made for statistical variation, especially in the case of findings for groups consisting of relatively few respondents, e.g., nonpublic school parents.

The findings of this report apply only to the U.S. as a whole and not to individual communities. Local surveys, using the same questions, can be conducted to determine how local areas compare with the national norm.

Sampling Tolerances

In interpreting survey results, it should be borne in mind that all sample surveys are subject to sampling error, i.e., the extent to which the results may differ from what would be obtained if the whole population surveyed had been interviewed. The size of such sampling error depends largely on the number of interviews.

The following tables may be used in estimating the sampling error of any percentage in this report. The computed allowances have taken into account the effect of the sample design upon sampling error. They may be interpreted as indicating the range (plus or minus the figure shown) within which the results of repeated samplings in the same time period could be expected to vary 95% of the time, assuming the same sampling procedure, the same interviewers, and the same questionnaire.

The first table shows how much allowance should be made for the sampling error of a percentage:

The table would be used in the following manner: Let us say that a reported percentage is 33 for a group that includes 1,000 respondents. We go to the row for "percentages near 30" in the table and across to the column headed "1,000."

The number at this point is 4, which means that the 33% obtained in the sample is subject to a sampling error of plus or minus four points. In other words, it is very probable (95 chances out of 100) that the true figure would be somewhere between 29% and 37%, with the most likely figure the 33% obtained.

In comparing survey results in two samples, such as, for example, men and women, the question arises as to how large a difference between them must be before one can be reasonably sure that it reflects a real difference. In the tables below, the number of points that must be allowed for in such comparisons is indicated. Two tables are provided. One is for percentages near 20 or 80; the other, for percentages near 50. For percentages in between, the error to be allowed for lies between those shown in the two tables.

Here is an example of how the tables would be used: Let us say that 50% of men respond a certain way and 40% of women respond that way also, for a difference of 10 percentage points between them. Can we say with any assurance that the 10-point difference reflects a real difference between men and women on the question? Let us consider a sample that contains approximately 750 men and 750 women.

Since the percentages are near 50, we consult Table B, and, since the two samples are about 750 persons each, we look for the number in the column headed "750" which is also in the row designated "750." We find the number 7 here. This means that the allowance for error should be seven points and that, in concluding that the percentage among men is somewhere between three and 17 points higher than the percentage among women, we should be wrong only about 5% of the time. In other words, we can conclude with considerable confidence that a difference exists in the direction observed and that it amounts to at least three percentage points.

If, in another case, men's responses amount to 22%, say, and women's to 24%, we consult Table A, because these percentages are near 20. We look in the column and row labeled "750" and see that the number is 5. Obviously, then, the two-point difference is inconclusive.

Design of the Sample

For the 1996 survey the Gallup Organization used its standard national telephone sample, i.e., an unclustered, directory-assisted, random-digit telephone sample, based on a proportionate stratified sampling design.

The random-digit aspect of the sample was used to avoid "listing" bias. Numerous studies have shown that households with unlisted telephone numbers are different in important ways from listed households. "Unlistedness" is due to household mobility or to customer requests to prevent publication of the telephone number. To avoid this source of bias, a random-digit procedure designed to provide representation of both listed and unlisted (including not-yet-listed) numbers was used.

Telephone numbers for the continental United States were stratified into four regions of the country and, within each region, further stratified into three size-of-community strata. Only working banks of telephone numbers were selected. Eliminating non-working banks from the sample increased the likelihood that any sample telephone number would be associated with a residence.

The sample of telephone numbers produced by the described method is representative of all telephone households within the continental United States.

Within each contacted household, an interview was sought with the youngest man 18 years of age or older who was at home. If no man was home, an interview was sought with the oldest woman at home. This method of respondent selection within households produced an age distribution by sex that closely approximates the age distribution by sex of the total population.

Up to three calls were made to each selected telephone number to complete an interview. The time of day and the day of the week for callbacks were varied so as to maximize the chances of finding a respondent at home. All interviews were conducted on weekends or weekday evenings in order to contact potential respondents among the working population. The final sample was weighted so that the distribution of the sample matched current estimates derived from the U.S. Census Bureau's Current Population Survey (CPS) for the adult population living in telephone households in the continental U.S. As has been the case in recent years in the Phi Delta Kappa/Gallup poll series, parents of public school children were oversampled in the 1996 poll. This procedure produced a large enough sample to ensure that findings reported for "public school parents" are statistically significant.

Conducting Your Own Poll

The Phi Delta Kappa Center for Professional Development and Services makes available PACE (Polling Attitudes of the Community on Education) materials to enable nonspecialists to conduct scientific polls of attitude and opinion on education. The PACE manual provides detailed information on constructing questionnaires, sampling, interviewing, and analyzing data. It also includes updated census figures and new material on conducting a telephone survey. The price is $55. For information about using PACE materials, write or phone Phillip Harris at Phi Delta Kappa, P.O. Box 789, Bloomington, IN 47402-0789. Ph. 800/766-1156.