Some participants filling out a trait questionnaire might not b motivated to answer carefully or truthfully . For example, some colleges and universities require introductory psychology students to participate in psychology experiments, many of which involve personality questionnaires. These volunteer participants may not be motivated to complete the questionnaires carefully; they may rush through the questionnaire answering randomly . Other participants may be motivated to answer correctly but might accidentally invalidate their answer sheets. For example, when participants are asked to put their answers on optical scanning sheets by filling in circle with a number 2 lead pencil, it is not uncommon for participants to inadvertently neglect to fill in a circle or two, which means that al subsequent answers are then incorrect as well. Another problem arises when, for some reason, the participant is not reading the questions carefully but is nevertheless providing answers. Perhaps the participant has difficulty reading, is tired, or even is hallucinating A common method for detecting these problems is to use an infrequency scale embedded within the set of questionnaire items. The infrequency scale contains items that all or almost all people will answer in a particular way . Using such items, if a person endorses more than one or two of these items in the "wrong" direction, then his or her test is flagged as suspicious. For example, o the Personality Research Form (Jackson & Messick, 1967), the infrequency scale contains items such as the following: "I do not believe that wood really burns," "I make all my own clothes and shoes," and "Whenever I walk up stairs, I always do so on my hands." These questions are answered "False" by over 95 percent o f
the people in samples from the United States and Canada. If a participant answers more than one or two of these as "T rue," we may begin to suspect that his or her answers do not represent valid information. Such a participant may be answering randomly , may have difficulty reading, or may be marking his or her answer sheet incorrectl .
Another technique used to detect carelessness is to include duplicate questions spaced far apart in the questionnaire. The psychologist can then determine the number of times the participant answered identical questions with dif ferent responses. If this happens often, the psychologist might suspect carelessness or another problem that invalidates the person' s answers.
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