Statistics and Compliance, II

This week (if a week is defined as "since last time I posted") I  learned that in case of a normal distribution, the mean/standard deviation is to be used. However, if the data is skewed, median/five number summary is to be used. I expect the latter (where median is the middle data) is better in skewed populations since it will be less affected by extreme cases. However, if you have two studies, and one gets results that are skewed while the other has a nice, normal distribution- how can you compare?

I realize this: I have never, ever ever ever seen the median being used to describe a population. I would say "and IQR even less so" but you can't have less than zero. Weirdly, I HAVE seen articles where the mean-standard deviation gives a value less than zero for something that can't be less than zero (pain scale, for example).

Fortunately, the article I read was great for continuing to wonder how to compare articles, and also continues the article from last week (again, week meaning last blog post). The article is Barriers to Treatment Adherence in Physiotherapy Outpatient Clinics: A Systematic Review by Jack et al.
The article narrows hundreds of potential articles to 20 cohorts and aims to identify barriers to adherence.

The punchline is that most studies found a low level of physical activity predicted low adherence to physical activity. Then a whole bunch of psychological reasons (depression, anxiety, etc), low social support and finally pain. The place of psychology in physical therapy/exercise is fascinating, as CBT and mindfulness courses seem to be creeping. But back to the main point. If you don't exercise, you probably won't exercise. I can't decide if that's wholly obvious to the point of silly, or really depressing to the point of depressing. We should start paying people to exercise.

And now for the technical aspect of comparing wildly different studies. What a fun mess! How do you define adherence? What is the lack of adherence percentage? Not known. Though the latter is anywhere between 14$-70% or above or below. And this was just in the introduction! The studies are so completely different in population type, size, and methods. Population type- they examined very different types of physical therapy such as pelvic floor, sports injury and osteoarthritis. The populations size in the studies varied extremely by size; one had 34 participants. Most had more.The methods were mostly questionnaire, but obviously different questionnaires, and thus comparing statistics really isn't quite right. Any guesses on how many studies used the median?