The biased sample
"There are more black men in prison than in college."
This is one of those two sided facts that the right will use to make a racist point and the left will use to make an antiracist point.
1) But is it even relevant?
Anyone have any suspicions?
This is a comparison of two groups. The group of all black men in college, and the group of all black men in prison.
Here's a thought. You go into college at 4 years, but in prison you could stay in for 10, 15, 20 years.
But to put it even clearer. The group of college age black men is the group from which the group of black men in college is drawn. Right?
2) Am I making a reasonable statement here?
Black men in college are college-aged.
What about black men in prison? Well, they could be any age (and are-- yes it's true youth commit more crime, but remember that people stay in prison for years and years).
So, next question:
3) What's a bigger group, the group of all black men or the group of college aged black men?
For the group of black men in college, we're drawing from the group of college aged black men. For the group of black men in prison, we're drawing from the group of all black men.
An even better example of this phenomenon, to stay on the racial issue, is one employed by new school racists: "American Blacks are lazy. Caribbean immigrants are black and their unemployment rate is lower than American Blacks. So it isn't racism-- it's cultural deficiency".
Well, at least they're off the 'genetic deficiency' bandwagon. Let's leave that aside. Let's leave aside also the assumption that unemployment and laziness are equivalent. This argument also depends on a biased sample.
Where's the bias? Well, those who can afford to immigrate are often those with some education, connections, and wealth. People with those things have a better chance of success. So the Caribbean example compares relatively wealthy, educated, connected immigrants with all American Blacks. Again, I'm attacking the statistical validity of the statement, not the moral bankruptcy of making these comparisons in the first place.
Lesson: Any time you hear someone compare groups, ask who's in the group and who's left out, and if that's convenient for the conclusion they're trying to convince you of.