Question

The Democratic National Committee wants to know how the general American population feel about the Democratic leadership in congress. The survey voters registered as Democrats. What source of error/bias may interfere most?

Selection bias

Recall bias

Interviewer bias

Non-differential misclassification (random error)

Answer 1

Here the answer would be selection bias. Because the sample selected for the study is biased towards the same political party. Their opinion is mostly positive because they can't provide an unprejudiced answer to a question which asks them about something they are already biased towards. This bias can be eliminated by random sampling. For example, you can select a study group randomly so that it contains supporters of all political parties.

Recall bias is seen in retrospective studies in which the participants are not able to recall and provide complete and accurate response to a question about their past events or experiences.

Interviewer bias occurs when interviewer is expecting a particular answer and phrases a question in such a format to get that answer . This can be eliminated by a written questionnaire.

Random error occurs due to limitations of measuring devices and can be reduced by repeated readings and taking the mean.