8-3 p394 n22
Original claim: the selection process is biased against Mexican-Americans because the proportion of Mexican-American jurors selected for grand jury duty is less than the proportion of Mexican-Americans (79.1%) in the general population in Hidalgo County, Texas
p < 0.5

The Null Hypothesis
H₀: p = 0.5

The Alternate Hypothesis
H₁: p < 0.5

A sample of n = 870 has 869 degrees of freedom.
For a left tailed test and a level of significance, α = 0.01
z_critical = -2.326

Data:
p^= 0.39
z_test = (0.39 - 0.5) ⁄ √0.5×0.5 ⁄ 870 = -6.489

Because -6.489 is IN the Critical Region, we Reject the Null Hypothesis and the statistical analysis of the data can support the original claim.

Conclusion:
The sample data SUPPORT the claim that the selection process is biased against Mexican-Americans because the proportion of Mexican-American jurors selected for grand jury duty is less than the proportion of Mexican-Americans (79.1%) in the general population in Hidalgo County, Texas