Marvin is looking for data to him with a new market research study assigned to him. when reviewing existing secondary data from a past research study, marvin should pay careful attention to:

how the secondary data were collected.

Explanation:

Secondary data refers to the data that is collected by other persons beside the researcher who actually use it. (in this context, it would be the data that is collected by other person than Marvin).

Sometimes, the  collection method could influence the data given by the samples and will shaken up the overall conclusions.

I'll give you an example.

In market research, companies often conducts research to find out consumers' preference toward a certain product. This preference could be given by the people through either public survey and private survey. Most people tend to give a more truthful answer if the data is collected through private survey since answering in public survey makes the people fear a chance that they will be judged by others.

a would be the answer