Of primary importance in constructing question items is to assure comprehension on the part of the respondent. Although the use of clear and easily understood language is a necessary step toward achieving that goal, simple language alone does not guarantee that the question is understood in the same manner by all respondents.
The literature examining comprehension problems in the design of income questions indicates that defining income constructs in a language easily understood by survey respondents is not easy (Moore et al., 1999). Terms that most researchers would consider to be well understood by respondents may suffer from differential comprehension. For example, Stinson (1997) found significant diversity with respect to respondents' interpretations of the term "total family income." Similarly, Bogen (1995) reported that respondents tend to omit sporadic self-employment and earnings from odd jobs or third or fourth jobs in their reports of income due to the respondents' interpretations of the term "income." These findings suggest the need for thorough testing of items among the population of interest to assess comprehension.
Comprehension of survey questions is affected by several factors, including the length of the question, the syntactical complexity, the degree to which the question includes instructions such as inclusion and exclusion clauses, and as the use of ambiguous terms. Consider, for example, the complexity of the following questions:
Example 1: Since your welfare benefits ended in (FINAL BENEFIT MONTH), did you take part for at least one month in any Adult Basic Education (ABE) classes for improving your basic reading and math skills, or General Education Development (GED) classes to help you prepare for the GED test, or classes to prepare for a regular high school diploma?
Example 2: In (PRIOR MONTH), did you have any children of your own living in the household? Please include any foster or adopted children. Also include any grandchildren living with you.
Example 3: Since (FINAL BENEFIT MONTH), have you worked for pay at a regular job at all? Please don't count unpaid work experience, but do include any paid jobs, including paid community service jobs or paid on-the-job training.
Each of these items is cognitively complex. The first question requires the respondent to process three separate categories of education, determine whether the conditional phrase "at least one month" applies only to the adult basic education classes or also to the GED and regular high school classes, and also attribute a reason for attending ABE ("improving reading and math skills") or GED classes. Separating example 1 into three simple items, prefaced by an introductory statement concerning types of education, would make the task more manageable for the respondent. Examples 2 and 3 suffer from the problem of providing an exclusion or inclusion (or in the case of example 3, both) clause after the question. Both would be improved by defining for the respondent what the question concerns and then asking the question, so that the last thing the respondent hears is the question. Example 2 may be improved by simply asking separate questions concerning own children, foster children, and grandchildren. Although questionnaire designers may be reluctant to add questions to an instrument for fear of longer administration times, we speculate that the administration of several well-designed short questions actually may be shorter than confusing compound questions that may require repeating or clarification.
With respect to question length, short questions are not always better. Cannell and colleagues (Cannell et al., 1977; Cannell et al., 1981) demonstrated that longer questions providing redundant information can lead to increased comprehension, in part because the longer question provides additional context for responding as well as longer time for the respondent to think about the question and formulate a response. On the other hand, longer questions that introduce new terms or become syntactically complex will result in lower levels of comprehension.
Comprehension can suffer from both lexical and structural ambiguities. For example, the sentence "John went to the bank" could be interpreted as John going to a financial institution or the side of a river. Lexical problems are inherent in a language in which words can have different interpretations. Although difficult to fix, interpretation can be aided through context and the respondent's usual use of the word (in this case, most likely the financial institution interpretation). Note that when constructing a question, one must consider regional and cultural differences in language and avoid terms that lack a clearly defined lexical meaning (e.g., "welfare reform"). Structural ambiguities arise when the same word can be used as different parts of speech--for example, as both a verb or an adjective in the sentence "Flying planes can be dangerous." Structural ambiguities most often can be repaired through careful wording of the question.
Questionnaire designers often attempt to improve comprehension by grouping questions so as to provide a context for a set of items, writing explicit questions, and, if possible, writing closed-ended items in which the response categories may aid in the interpretation of the question by the respondent. In addition, tailoring questions to accommodate the language of specific population subgroups is feasible with computer-assisted interviewing systems.
Comprehension difficulties are best identified and repaired through the use of selected pretesting techniques such as cognitive interviewing or expert panel review (e.g., Presser and Blair, 1994; Forsyth and Lessler, 1991). Requesting respondents to paraphrase the question in their own words often provides insight into different interpretations of a question; similarly, the use of other cognitive interviewing techniques such as think-aloud interviews or the use of vignettes can be useful in identifying comprehension problems as well as offer possible alternative wording options for the questionnaire designer.
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