If what you're trying to measure is how someone feels, it might be necessary to ask them how they feel - and what they feel influence that. If one person thinks

If what you're trying to measure is how someone feels, it might be necessary to ask them how they feel - and what they feel influence that. If one person thinks job stress make them unhappy, that might be anecdotal - if seven hundred of a thousand say work makes them unhappy - that might be more towards the "data" end of the spectrum?