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Services and Resources for Children and Young Adults in Public Libraries
NCES: 95357
September 1995

Appendix A: Survey Methodology and Data Reliability

In spring 1994, two national probability samples of 890 public library outlets each were selected for this study from the 1991 Public Library Universe System obtained from the National Center for Education Statistics. Both the 8,837 central and the 6,542 branch libraries were sampled for the survey. One sample received the Survey on Library Services for Children in Public Libraries, and the second sample participated in the Survey on Library Services to Young Adults in Public Libraries.

Sample Selection Libraries, Library

The sample was stratified by Census region (Northeast, Midwest, South, and West), metropolitan status (urban, suburban, rural), type of outlet (central/single outlet, branch) and size of library (as measured by the estimated size of the population served by the outlet).

Response Rate

In March 1994, questionnaires (see Appendix C) were mailed to 1,780 library outlets. Of the 890 public library outlets sampled for the children's services survey, 32 were found to be out of the scope of the study (not a public service library or closed), and 36 of 890 in the young adult study sample were out of scope for the study. Telephone follow up was initiated in late April; data collection was completed by early June with 815 libraries in the children's sample and 800 in the young adult sample. Thus, the final response rates were 94 percent for the survey on children's services and 93 percent for the survey on young adult services in public libraries. Item nonresponse ranged from 0.0 percent to 0.7 percent.

Sampling and Nonsampling Errors

The response data were weighted to produce national estimates. The weights were designed to adjust for the variable probabilities of selection and differential nonresponse. A final poststratification adjustment was made so that the weighted library counts equaled the corresponding estimated counts from the Library Universe frame within cells defined by the size of library, region, and metropolitan status. The findings in this report are estimates based on the samples selected and, consequently, are subject to sampling variability.

The survey estimates are also subject to nonsarnpling errors that can arise because of nonobservation (nonresponse or noncoverage) error, errors of reporting, and errors made in collection of the data. These errors can sometimes bias the data. Nonsarnpling errors may include such problems as the difference in the respondents' interpretation of the meaning of the question; memory effect; misrecording of responses; incorrect editing, coding, and data entry; differences related to the particular time the survey was conducted; or errors in data preparation. While general sampling theory can be used in part to determine how to estimate the sampling variability of a statistic, nonsampling errors are not easy to measure and. for measurement purposes. usually require that an experiment be conducted as part of the data collection procedure or that data external to the study be used.

To minimize the potential for nonsampling error, the questionnaires, which were extensively reviewed and largely developed by two panels of expert practitioners, were pretested with public libraries like those that completed the survey. During the design of the survey and the survey pretest, an effort was made to check for consistency of interpretation of questions and to eliminate ambiguities. The questionnaires and instructions were extensively reviewed by the National Center for Education Statistics and the Office of Library Programs. Manual and machine editing of the questionnaire responses were conducted to check the data for accuracy and consistency. Cases with missing or inconsistent items were recontacted by telephone. Imputation for item nonresponse was not implemented, as item nonresponse rates were less than 1 percent (for nearly all items, nonresponse rates were less than 0.5 percent). Data were keyed with 100 percent verification.

Variances

The standard error is a measure of the variability of estimates due to sampling. It indicates the variability of a sample estimate that would be obtained from all possible samples of a given design and size. Standard errors are used as a measure of the precision expected from a particular sample. If all possible samples were surveyed under similar conditions, intervals of 1.96 standard errors below to 1.96 standard errors above a particular statistic would include the true population parameter being estimated in about 95 percent of the samples. This is a 95 percent confidence intend. For example, the estimated percentage of libraries that offer story times for children is 90 percent, and the estimated standard error is 1.6 percent. The 95 percent confidence interval for the statistic extends ilom [90 - (1.6 times 1.96) to 90 + (1.6 times 1.96)], or from 86.9 to 93.1 percent.

Estimates of standard errors were computed using a technique known as jackknife replication. As with any replication method, jackknife replication involves constructing a number of subsamples (replicates) from the full sample and computing the statistic of interest for each replicate. The mean square error of the replicate estimates around the full sample estimate provides an estimate of the variance of the statistic (see Welter 1985, Chapter 4). To construct the replications, 30 stratified subsamples of the full sample were created and then dropped one at a time to define 30 jackknife replicates. A proprietary computer program (ESVAR), available at Westat, Inc., was used to calculate the estimates of standard errors. The software runs under IBM/OS and VAX/VMS systems.

Background Information

The survey was conducted under contract by Westat, Inc., using the NCES Fast Response Survey System (FRSS). Westat's Project Director was Elizabeth Farns, and the Associate Project Director and Survey Manager was Sheila Heaviside. Judi Carpenter was the NCES Project Officer. The data were requested by Ray Fry and Christina Dunn of the Office of Library Programs, U.S. Department of Education.

This report was reviewed by the following individuals:

Outside NCES.

  • Mary K. Chekon, Rutgers University
  • Susan Roman, Association for Library Services to Children,
  • American Library Association
  • Mary Jo Lynch, Office for Research Statistics, American Library Association

Inside NCES.

  • Steve Broughman, Elementary/Secondary Education Statistics Division
  • Michael Cohen, Statistical Services and Methodological Research Branch
  • Daniel Kaspmyk, Elementary/Secondary Education Statistics Division
  • Carrel Kindel, Library Statistics Group, Postsecondary Education Statistics Division
  • Marilyn McMillen, Elementary/Secondary Education Statistics Division
  • Jeffrey Williams, Library Statistics Group, Postsecondary Education Statistics Division

For more information about the Fast Response Survey System or the Surveys of Library Services for Children and Young Adults in Public Libraries, contact Judi Carpenter, Elementary/Secondary Education Statistics Division, Office of Educational Research and Improvement, National Center for Education Statistics, 555 New Jersey Avenue, NW, Washington, DC, 20208-5651, telephone (202) 219-1333.

References

The WESVAR Procedures. 1989. Rockville, MD: Westat Inc.

Woiter, K. 1985. Introduction to Variance Estimation. Springer-Verlag.

Glossary of Terms

Children's specialist/librarian - library staff member who by education or training (formal or inservice) has a background in library services specifically for children.

Young adult specialist/librarian - library staff member who by education or training (formal or inservice) has a background in library services for young adults.
Youth services specialist./librarian - library staff member who by education or training (formal or inservice) has a background in library services for both children and young adults.

Sample Universe and Classification Variables

Metropolitan status

Urban - primarily serves a central city of a Standard Metropolitan Statistical Area (SMSA).

Suburban - seines an SMSA of a central city, but not primarily its central city.

Rural - does not serve an SMSA.

Geographic region

Northeast - Connecticut, Delaware, District of Columbia, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania Rhode Island, and Vermont.

Southeast - Alabama, Arkansas, Florida, Georgia Kentucky, Louisiana, Mississippi, North Carolina, South Carolina Tennessee, Virginia, and West Virginia.

Central - Illinois, Indian& IOWL Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota. Ohio, South Dakota, and Wisconsin.

West - Alaska, Arizona, California Colorado, Hawaii, Idaho, Montana Nevada, New Mexico, Oklahoma Oregon, Texas, Utah. Washington, and Wyoming.

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