On the first day of trout season a team of biologists went with local trout anglers to the Macawber River. Each angler who caught at least 2 trout chose exactly 2 of these trout for the biologists to weigh. A total of 90 fish were weighed. The measurements show that at the beginning of this season the average trout in the Macawber River weighed approximately 1. 6 kilograms.
The reasoning above is most vulnerable to criticism on the grounds that it makes a generalization from a sample that is unlikely to be representative.