Q:

Of the subjects in our experiment, 50% are/were male

I'm writing a report and need to decide whether to use present or past tense: 
Of the subjects in our experiment, 50% are/were male, 50% have/had at least a college degree, 90% are/were employed...
According to the 2010 US Census, 49% of the population are/were male, and 27% have/had at least a college degree, 91% are/were employed...
Should the words in gray be in present tense or past tense? Or is it immaterial as long as I'm consistent? (Note: statistics are made up)

A:

The quick way to answer this question is to look at what other papers in your field do. But, most likely, they will use the past tense. 
My copy of the Publication Manual of the American Psychological Association (6th ed.) says:

Select tense carefully. Use the past tense to express an action or a condition that occurred at a specific, definite time in the past, as when discussing another researcher's work and when reporting your results.

(Bold in original; italics are mine).
Secondly, naturally, some of these states can change. While no one is likely to change what degrees they have, it is conceivable that some of your subjects will have lost their job, died, or changed their gender identity between collection and publication.

