Final answer:
The appropriate strategy for dealing with missing information on a completed questionnaire is to either overlook the missing information and code the remaining answers or substitute information based on the responses of similar respondents. So, the correct options are d. both a and c only.
Step-by-step explanation:
The question asks for a strategy that might not be appropriate for dealing with missing information on a completed questionnaire. Among the given options, throwing out the entire completed questionnaire (option a) would not be an appropriate strategy. This is because throwing out the entire questionnaire would result in the loss of all the data collected, which could be valuable for the study.
Instead, researchers should consider other strategies such as overlooking the missing information and coding the remaining answers (option b) or substituting information based on the responses of similar respondents (option c). For example, if a questionnaire is missing information about a respondent's income, a researcher could look at the responses of similar respondents and estimate an income range based on their answers. Therefore, the correct option is d. both a and c only.