Evidence of shift work and detrimental effects on health.
Quite a lot of work has now been carried out on this subject, but getting the airlines to admit it's an issue is quite a separate matter. Even when knowingly stepping into areas of poor industry practice, some of them still do it...........
My own outfit for example recognises in its Ops Manual that 24 hour layover periods are poor practice, and yet routinely schedules them.
Sorry to say but the industry generally responds reactively to problems, as opposed to proactively. The harsh reality recognised by the realists (as opposed to cynics) amongst us, is that as a business we just don't kill enough people. Not that anyone wants to, but history shows that is the only time things change.
When we get it wrong we sadly have the ability to destroy many hundreds of lives, and yet still poor industry practice prevails in such basic issues as fatigue. We've decided quite correctly that we don't want drunk pilots flying our planes, but have we genuinely decided that we don't want tired / fatigued pilots flying them? And please let's not get into the semantics of tired vs. fatigued, let's just accept that widespread industry support has yet to mature to the point of acceptance of this problem.
In the developed world (name your own choice of the globe as you see fit) these battles are maybe easier to fight with logic and outside support, but translate that to parts of the industry where lots of money, many new aircraft and rapid company growth, combined with antiquated thinking and feeble levels of managerial accountability, and the stage is set.
Indeed, it may appear that the chickens are all ready coming home to roost......