Also, studies are instrinsicly problematic. One of my favorite college classes was a sociology class run by a man who professionally conducted surveys and just taught on the side. He'd love to tell us that you know what answers your employer wants, so you need to ask the right questions and word them in a certain way to get the results you are looking for. Because nobody hires firms who tell their employers what they don't want to hear.

Besides the fact that people just aren't good at self-reporting.

And studies are huge in pharmaceuticals. Like antidepressants, a personal pet peeve of mine. They'd ask how you felt before taking the meds on a scale 1-5, ask how you feel on meds 1-5. Besides that being totally subjective and ignoring a whole lot of variables, there's a phenomenon where depressed people's mood improves simply by having attention brought to the problem. It's optimism. They know this happens and they ask loaded questions like that anyways knowing it'll skew results.