"You're backing it up with your own personal anecdote?"
No. I provided a counterexample that falsifies an implicit assumption of the 6-year cutoff model of the college dropout rate. If you measure your dropout rate as the percentage of students who have not graduated within 6 years of enrollment, it is provably true that your measurement is an overestimate of the true value.
"Maybe the reason why the 6 year cutoff is so often used is because someone already crunched the numbers and found it was good enough?"
If someone had already crunched the numbers, the appropriate correction factor to apply to the 6-year measurement would be well-known and, instead of reporting the 6-year cutoff value, a distribution-corrected 6-year cutoff value would have been reported instead. If nobody crunched the numbers to find out what the characteristics of the distribution's tail are, then the methodology is sloppy. If a correction factor was applied but not explicitly mentioned where the value is reported, then the reporting is sloppy. Either way, a reasonable person is justified in regarding the reported value as merely an upper bound on the dropout rate and rejecting the assertion that it is an accurate measurement of the true value.
No. I provided a counterexample that falsifies an implicit assumption of the 6-year cutoff model of the college dropout rate. If you measure your dropout rate as the percentage of students who have not graduated within 6 years of enrollment, it is provably true that your measurement is an overestimate of the true value.
"Maybe the reason why the 6 year cutoff is so often used is because someone already crunched the numbers and found it was good enough?"
If someone had already crunched the numbers, the appropriate correction factor to apply to the 6-year measurement would be well-known and, instead of reporting the 6-year cutoff value, a distribution-corrected 6-year cutoff value would have been reported instead. If nobody crunched the numbers to find out what the characteristics of the distribution's tail are, then the methodology is sloppy. If a correction factor was applied but not explicitly mentioned where the value is reported, then the reporting is sloppy. Either way, a reasonable person is justified in regarding the reported value as merely an upper bound on the dropout rate and rejecting the assertion that it is an accurate measurement of the true value.