# Thread: Jury Selection Discrimination Theory Problem

1. ## Jury Selection Discrimination Theory Problem

In 1972 Mr Partida, a Mexican-American, was convicted of burglary by a jury in a particular county in Texas. Mr Partida’s lawyers, appealed the conviction on the grounds that the jury must havebeen selected in a discriminatory (and thus non-random fashion) because it had a disproportionately small number of Mexican-Americans on it.

They based their argument on the following two pieces of information.

First, a recent census had shown Mexican-Americans made up 79.1% of adults in the population in that county and that this fact was widely accepted.

Second, in a sample of court cases in the county involving a total of 870 jury members, only 39% were Mexican-Americans.

Assume that we will conclude that jury selection in the county was discriminatory if there is less than a 1% chance that a sample proportion of 39% (or less) would result from random selection from a population where the proportion was 79.1%. If you were a Justice of the US Supreme Court, what would your finding be? Would you find that there probably was discrimination in jury selection in the county?

Any help with this one guys? I have no idea where to start! Too many percentages for me to handle! =(

Thanks

2. Originally Posted by mibamars
In 1972 Mr Partida, a Mexican-American, was convicted of burglary by a jury in a particular county in Texas. Mr Partida’s lawyers, appealed the conviction on the grounds that the jury must havebeen selected in a discriminatory (and thus non-random fashion) because it had a disproportionately small number of Mexican-Americans on it.

They based their argument on the following two pieces of information.

First, a recent census had shown Mexican-Americans made up 79.1% of adults in the population in that county and that this fact was widely accepted.

Second, in a sample of court cases in the county involving a total of 870 jury members, only 39% were Mexican-Americans.

Assume that we will conclude that jury selection in the county was discriminatory if there is less than a 1% chance that a sample proportion of 39% (or less) would result from random selection from a population where the proportion was 79.1%. If you were a Justice of the US Supreme Court, what would your finding be? Would you find that there probably was discrimination in jury selection in the county?

Any help with this one guys? I have no idea where to start! Too many percentages for me to handle! =(

Thanks
I would throw the case out as there is no evidence presented that the population that juries are selected from is that same as that of the "recent census". Also you need to show that the preferences of the lawyers in challenging the jury candidates were not biasing jury composition. etc ...

CB

3. Any mathematical evidence to support this?

4. Originally Posted by mibamars
Any mathematical evidence to support this?
It works the other way round, a justice of the Supreme Court would require evidence that what is implied in the question is a valid procedure, and none is presented, you are not even told to assume what is needed to make this valid.

So the question setter or you must state the additional assumptions to make the implied calculations valid.

But in an actual court this argument would still be thrown out unless those assumptions are demonstrated to be valid.

CB

5. Originally Posted by mibamars
In 1972 Mr Partida, a Mexican-American, was convicted of burglary by a jury in a particular county in Texas. Mr Partida’s lawyers, appealed the conviction on the grounds that the jury must havebeen selected in a discriminatory (and thus non-random fashion) because it had a disproportionately small number of Mexican-Americans on it.

They based their argument on the following two pieces of information.

First, a recent census had shown Mexican-Americans made up 79.1% of adults in the population in that county and that this fact was widely accepted.

Second, in a sample of court cases in the county involving a total of 870 jury members, only 39% were Mexican-Americans.

Assume that we will conclude that jury selection in the county was discriminatory if there is less than a 1% chance that a sample proportion of 39% (or less) would result from random selection from a population where the proportion was 79.1%. If you were a Justice of the US Supreme Court, what would your finding be? Would you find that there probably was discrimination in jury selection in the county?

Any help with this one guys? I have no idea where to start! Too many percentages for me to handle! =(

Thanks
Disregarding any questions about legal procedure, the number of Mexican-Americans on the juries, if chosen randomly from all adults in the county, should have a Binomial distribution with n = 870 and p = 0.791. The observed number was evidently 0.39 * 870 = 339. So we would like to know $\displaystyle \Pr(X \leq 339)$ when X has the stated distribution. You might find a Normal approximation useful.

P.S. Evidently the court found the evidence for discrimination convincing. See
http://www.law.cornell.edu/supct/htm...0_0482_ZS.html