Some characteristics of self-report questionnaires can result in bias in responding. When a test item or a questionnaire is biased, the observed scores form an imprecise measurement of reality as a consequence of systematic errors of measurement. Causes of such bias are: unclear instructions, vague wording of the test items, culture-bound item content, suggestive questions, framing of questions, social desirability of certain answers, faking good, faking bad and the recall bias.