Asking for proof through studies for a hobby that is not a profession is a near impossible task to accomplish.
Anecdotal evidence and popular trends is about all we have to go on around here unless the study was done for something else and then translated for our uses.
I agree. However, some ideas seem to last in this hobby without even solid anecdotal evidence. Like garlic curing ich :headwallblue: The idea that a stressed fish is more likely to contract ich is clearly valid, but there is not good evidence (anecdotal or other) that temperature fluctuations cause stress to fish. I would guess this idea comes from sellers who post a temperature somewhere in the middle of the temperatures the fish typically experience in the wild, knowing that heaters will vary significantly from that. Hobbyist then panic whenever their temperature strays from that number.