Questionnaires

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  A lot of data can be collected from large numbers of people quickly and cheaply compared to an interview as they require no specialist training.
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  Fewer investigator effects
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  Ppts are more likely to answer honestly.
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  Lowered validity- due to leading questions
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  Social desirability bias
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  The sample is biased because only motivated people fill in questionnaires.
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  Participants may misunderstand questions without a researcher to explain.