This article makes a case for such an adjustment when looking at MS stats and clinical trials. If one takes this information at face value, I would be trying to run my clinical trials for new drugs/procedures during the coldest times of the year in the coldest places as my end points so I could hide/offset some negatives in the positive impact of the change in temperature. Of note, the studies used for this were small with 40 MS patients for one time period and 45 MS patients from a different pool at the second point in time. There are some with MS who can’t take the cold but are fine in the heat, the opposite of my reaction. Had there been a couple of them in the trial, the results could have come back opposite what is being published here.
I am not saying I disbelieve the results or think they don’t point to some thing of importance when trying to determine the validity of different tests and trials. In fact, based on personal experience, I would believe the results most likely valid enough to warrant further testing to determine a seasonal adjustment. In a large study, this type of seasonal adjustment may lead to more correct identification of significant trends rather than those trends caused solely by weather.
One last note on the structure of the study’s results: they are reporting a significant correlation. There is a saying “correlation does not equal causation.” For example, in a NY City study, ice cream sales increased as outdoor violent crime increased. Does ice cream cause us to murder each other? We may all scream for ice cream, but murder? Isn’t it just as plausible to think people buy and eat ice cream during the spring, summer, and fall when going outside is comfortable. Then they buy less ice cream in the winter when they stay inside and thus aren’t outside to either perpetrate violent crimes or be victims of them? (note the seasonal adjustment needed for even this study)