Sim study.
I think, but I'm not completely sure, that the Sim study ended up with an unforecast result.
Two sets of crews compared.
First set - consisted of two people, Captain and F/O called in from home. Refreshed. Not sleep deprived.
Second set - had all just done a 9 day JFK pattern. Capt and F/O [only] went straight into the Sim on arrival from LAX. No rest. Eyeballs hanging out.
But - guess what - The tired crews outperformed the fresh ones from home.
Hmmm. Why? The tired pairings had just been working together for 9 days, including a couple of demanding two man sectors together across the US to JFK and back and had gotten used to each other's style of operation.
The two from home had quite possibly never met each other and were coming in 'cold'.
About that time, it all went very quiet on the study. Didn't hear anything about it after that.
[Also, possibly, the crews might have been mismatched in terms of operational experience. The JFK crews would most probably have been senior guys and the guys on A days quite possibly junior in rank. Whether that is a + or a - you are free to debate.]