In: Statistics and Probability
A public opinion poll surveyed a simple random sample of 1000 voters. Respondents were classified by gender (male or female) and by voting preference (Republican, Democrat, or Independent). Results are shown in the contingency table below.
VOTING PREFERENCES
Rep Dem Ind Row Total
Male 350 075 25 450
Female 275 240 35 550
Column Total 625 315 60 1000
Is there a gender gap? D3 the men's voting preferences differ significantly from the women's preferences? Use a 0.05 level of significance.
Answers should be in word format please
Solution:
Let us use Chi-square test for independence to analyze the result.
The observed frequency counts is as follows:
Voting Preferences | ||||
Rep | Dem | Ind | Row total | |
Male | 350 | 75 | 25 | 450 |
Female | 275 | 240 | 35 | 550 |
Column Total | 625 | 315 | 60 | 1000 |
Step 1:State the null and alternative hypothesis.
Ho:Gender and voting preferences are independent.
Ha:Gender and voting preferences are not independent.
Step 2:Determination of degree of freedom, the expected frequency count and test statistics.
df=(r-1)*(c-1)=(2-1)*(3-1)=1*2=2
Formula to find expected frequency count=(nr*nc)/n where nr= row total, nc=column total and n=total sample size
Expected frequency count | ||||
Rep | Dem | Ind | Row total | |
Male | (450*625)/1000=281.25 | (450*315)/1000=141.75 | (450*60)/1000=27 | 450 |
Female | (550*625)/1000=343.75 | (550*315)/1000=173.25 | (550*60)/1000=33 | 550 |
Column Total | 625 | 315 | 60 | 1000 |
Formula to find test statistics is given as follows:
X2=(O-E)2/ E
Rep | Dem | Ind | |
Male | (350-281.25)2/281.25=16.81 | (75-141.75)2/141.75=31.43 | (25-27)2/27=0.15 |
Female | (275-343.75)2/343.75=13.5 | (240-173.25)2/173.25=25.72 | (35-33)2/33=0.12 |
X2=16.81+31.43+0.15+13.5+25.72+0.12=87.98
X2 Critical value=5.991
Since X2 observed value=87.98 is greater than X2 critical value, we reject the null hypothesis and conclude that the gender and voting preferences are not independent.