Public Policy Polling Institute’s survey of 700 likely voters conducted in April 2009 found that Obama’s approval rating was 53% , down from 55% a month ago (in March 2009). Assume that the size of the sample (700) is the same for the April and March polls, and that 53 and 55% are the sample proportions in April and March, respectively.  Sample summary statistics are provided below:

Month           Sample size      Sample Proportion (in percent

March................700                  55

April ................. 700                  53

Is the decrease in approval rating from March to April statistically significant? Conduct a one sided significance test for the decrease assuming a significance level alpha = 0.05. Our suspicion is that the true (national) approval rating in April is less than the true approval rating in March. Write down the following:

1. the null and alternative hypothesis
2. the value of the test statistic
3. The P-value
4. Draw the conclusion about whether the decrease in Obama’s approval rating from March to April is statistically significant at alpha = 0.05.    

Answer rating: 100% (QA)

1 Let po be the population proportion of Obamas approval rating in April 2009 Then ... View the full answer