Survey of Statistical Methods. April 25, 2005. Sample Problem.
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April 25, 2005
When group membership makes a difference, the dependent relationship is indicated by one group having a higher proportion than the proportion for the total sample.
When the variables are independent, the proportion in both groups is close to the same size as the proportion for the total sample.
Note: chi-square must be calculated on actual count data, not substituting percentages, which would have the effect of pretending the sample size is 100.
1 = Republican
2 = Democrat
1 = For
2 = Against
3 = Undecided
Analyze – Descriptive Statistics -- Crosstabs
Figure 1a. Histogram showing the association between political affiliation and attitude toward the bill. A Chi-Square Test of Independence revealed a significant relationship between these variables [X2(2)=6.0: p=.05]. Democrats were found to have a more favorable attitude toward the bill than Republicans.
Figure 1b. Histogram showing the association between political affiliation and attitude toward the bill. A Chi-Square Test of Independence revealed a significant relationship between these variables [X2(2)=6.0: p=.05]. Republicans were found to have a more unfavorable attitude toward the bill than Democrats.
Critical X2 =
Post-Hoc analysis for a Chi Square Test of IndependenceWhich Cell or Cells Caused the Difference