Validity of Surveys-Participation 2

According to  survey methodology, what are factors that can influence the way people respond to survey questions?  What can researchers do to help mitigate these sources of variation in responses?     

Reference:

Neutens, J. J., & Rubinson, L. (2014). Research techniques for the health sciences (5th ed.).San Francisco, CA: Pearson Benjamin Cummings.

In 100 words APA format