• Research on understanding mode effects, including ways in which mixed-mode designs affect both nonresponse and measurement errors and the impact of modes on reliability and validity.
The panel notes that there has been increasing appreciation of the role of nonresponse bias, but this only draws attention to the lack of a comprehensive theory of nonresponse bias. A more comprehensive theory would help further a basic understanding of the relationship between response rates and nonresponse bias, enhance the understanding of such bias, and aid in the development of adjustment techniques to deal with bias under differing circumstances. A unifying theory would assure that comparisons of nonresponse bias in different situations would lead to the development of standard nomenclatures and approaches to the problem. To assist in the development of such a theory, the report sugests a need for:
• Research on the relationship between nonresponse rates and nonresponse bias and on the variables that determine when such a relationship is likely.
• Research to examine both unit and item nonresponse bias and to develop models of the relationship between nonresponse rates and bias.
• Research on the impact of nonresponse reduction on other error sources, such as measurement error.
• Research to quantify the role that nonresponse error plays as an overall component of total survey error.
• Research on the differential effects of incentives offered to respondents (and interviewers) and the extent to which incentives affect nonresponse bias.
Finally, research that is needed to identify those plans, policies, and procedures that would assist in overcoming the problem:
• Research to establish, empirically, the cost–error trade-offs in the use of incentives and other tools to reduce nonresponse.
• Research on the nature (mode of contact, content) and the effects of the contacts that people receive over the course of a survey, based on data captured in the survey process.
• Research leading to the development of minimal standards for call records and similar data in order to improve the management of data collection, increase response rates, and reduce nonresponse errors.
• Research on the structure and content of interviewer training as well as on the value of continued coaching of interviewers. Where possible, support should be given to experiments designed to identify the most effective techniques.