Ch. 28 Chi-square test
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Ch. 28 Chi-square test • Used when the data are frequencies (counts) or proportions for 2 or more groups. • Example 1 1. O bserved frequencies Eye Right Left T otal H and Right 18 5 Left 2 2 T otal
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Ch. 28 Chi-square test. Used when the data are frequencies (counts) or proportions for 2 or more groups. Example 1. 5. Calculate ((observed-expected)^2) expected 6. Calculate Chi-square = sum of the values from step 5. The degrees of freedom = - PowerPoint PPT Presentation
Transcript of Ch. 28 Chi-square test
Ch. 28 Chi-square test
• Used when the data are frequencies (counts) or proportions for 2 or more groups.
• Example 11. Observed frequencies
EyeRight Left Total
Hand Right 18 5Left 2 2Total
2. Observed percents
EyeRight Left Total
Hand Right 90% 71%Left 10% 29%Total
3. Expected percents
EyeRight Left Total
Hand Right 85% 85%Left 15% 15%Total
4. Expected frequencies
EyeRight Left Total
Hand Right 17 6Left 3 1Total
5. Calculate ((observed-expected)^2)
expected
6. Calculate Chi-square = sum of the values from step 5. The degrees of freedom =
(# rows - 1)x(# columns – 1). Find the p-value using the Chi-square table.
Activity: Titanic survival data
• Example 2: Titanic survival data grouped by class.
1. Observed frequencies
Class1st 2nd 3rd Total
Surivor Yes 203 118 178No 122 167 528Total
2. Observed percents
Class1st 2nd 3rd Total
Surivor Yes 62%NoTotal
Null hypothesis: Class and survival are independent. In other words, everyone had the same chance of survival.
Use the bootstrap method to estimate the proportions in the box based on the observed data.
Null hypothesis: The proportion of “yes” in every class is the same as the overall proportion = 38%.
3. Expected percents
Class1st 2nd 3rd Total
Surivor Yes 38%No 62%Total
4. Expected frequencies
Class1st 2nd 3rd Total
Surivor Yes 499No 817Total 325 285 706 1316
• Chi-square =
• P-value =
