Akey disadvantage to self-report measures is that

A key disadvantage to self-report measures is that social desirability bias can distort findings, compromising the validity of a study. Social desirability bias refers to the phenomenon where participants of a study are dishonest and answer in a way that makes them seem socially desirable. Other disadvantages of self-report methods such as questionnaires include:

1) Wrong answers due to forgetting or poor recall
2)Questionnaires might be misunderstood- leading to low validity of study
3)Low response rates- this is common in questionnaires. 

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