Structural Determinants of Mail Survey Response Rates Over a 12-Year Period, 1988-1999

One of the most nagging and difficult questions to answer about response rates to mail surveys concerns whether response rates have been declining in recent years, as they appear to be for telephone surveys. Another question about which little is known is the extent to which characteristics of particular survey populations influence the level of response that can be achieved when using particular design and implementation procedures. Our purpose in this paper is to provide tentative answers to these questions. Over a 12-year period, from 1988 through 1999, 102 sample surveys of visitors to U.S. National Parks were conducted by the same sponsor using very similar questions about visitor experiences in the park, and a common set of implementation procedures, except for two features" the length of each questionnaire and the number of replacement mailings. Statistically it is possible to estimate the effect of year of study on response rates for these two major variations in study procedures found in the past to be a major determinant of final response rates (Heberlein and Baumgartner, 1978; Dillman et al., 1974; Dillman, 2000). In addition, the visitors to each national park constitute a unique survey population, differing with regard to average age, distance traveled, time spent and other structural features that might influence response rate. This paper provides results from regression analyses in which each park becomes a unit of observation. The 102 response rates (one per park) are then regressed on these structural variables, year of study, questionnaire length, and number of replacement questionnaires in order to understand their individual and combined effects on survey response rates.