What is the purpose of describing the demographic data in resarch?

APA Format and use of Journal articles are mandatory

a. Demographic data are collected for every study. What is the purpose of describing the demographic data in resarch? (500+ words, APA style, at least 1 journal article)

b. There is a tendency for novice researchers to develop their own instrument if they cannot readily find one. How might you respond to a peer or manager who asks you to help develop a new tool to collect patient data on anxiety prior to cardiac catheterization? (500+ words, APA style, at least 1 journal article)