Originally Posted by
exerda
To be fair, with self-reporting from FTers, there's going to be a selection bias present in the data regardless of how large the data set is--unless as you say it covered all pax and flights.
No doubt about that.
What bothers me, though, is that some people apparently come to the table with the notion that selection bias = completely unusable results.
The key is to think critically about the selection bias and what it's likely to do to the data. Take brain imaging studies, for example. Most subjects in those studies are 18-26 year old smart people. (I'll let you figure out why.) That's some pretty big selection bias. And yet, we accept it and move on, because the bias should have no predicted effect on the research questions being studied. To the extent that there are concerns, these are noted and recognized as limitations of the study.
My hope is that people here can move beyond their initial skepticism and accept the data on DidItClear while recognizing that the limitations on the data are themselves limited.