Question

The web analyst from Zulily, was asked a follow up question by her boss. Her boss said she was wondering how the conversion rate for this year compared to a year ago at the same time. This year Zulily had a great deal of messaging on the website regarding "Back to School" themes. The analyst extracts the data and finds the following:

2019 in the three week time period ending 8/2 there were 28,225 visits and a 3.2% conversion rate

2018 in the three week time period ending 8/3 there were 30,875 visits and a 2.96% conversion rate

She constructs two confidence intervals for the difference between two means

90% confidence interval (.2400%, .4742%)

95% confidence interval (-.0391%, .5191%)

How should she interpret these results and advise her boss the meaning of the results?

Answer 1

The 90% confidence interval for the difference between the means of the conversion rate for both years is (0.2400%, 0.4742%)

and 95% confidence interval for the difference between the means of the conversion rate for both years is (-0.0391%, 0.5191%)

The 90% confidence interval does not contain 0, so she can not interpret the means of the conversion rate for both years is the same. That is there is a difference between the means of the conversion rate of both years.

The 95% confidence interval contains 0, so she can interpret the means of the conversion rate for both years is the same. That is there is no difference between the means of the conversion rate of both years.