Last answered:

22 Apr 2024

Posted on:

12 Apr 2024


Statistics Practice exam 3 Question 6

Hello, I see two others have asked this question without any instructor responding, hoping third time is a charm here. 

I have gone over the explanation of question 6 of the Practice exam at the end of the Confidence Interval section and understand all the steps that lead up to the solution. However, whenever I plug in all the individual components (difference point estimator, t-statistic, standard error: (12.71%-3.63%) - 1.73 x .04  ) I get the wrong answer. No matter what adjustments I make where I think I may have made an error, I don't get the same CI of (1.84%,16.32%) or anywhere near it. 

Have I understood the last step incorrectly? Ironically it is also the only practice exam explanation that doesn't write out the solution in numbers to be able to easily visualize what the solution in writing claims. Could an instructor please address this and explain and write out the solution in numbers? 


1 answers ( 0 marked as helpful)
Posted on:

22 Apr 2024


Hi Lae!

Please accept my apologies for the delayed response. We had to investigate the issue in further detail.

Keep in mind that the obtained results may differ slightly due to how the numbers are rounded. Consider this:

The precise difference in means between Quant C and Quant B is 0.12706 minus 0.03628, which equals 0.09078, or 9.078%. The precise calculation of the standard error can yield slightly different results that may round to 4%. A calculated standard error of 0.041849711 can be approximated as 0.04. Multiplying this standard error by the critical value of 1.73 gives approximately 0.0724 or 7.24%. Using this margin of error, the lower bound of the confidence interval is derived by subtracting 7.24% from 9.078%, resulting in 1.838%, and the upper bound by adding 7.24% to 9.078%, resulting in 16.318%. Rounded, these values are 1.84% and 16.32%, respectively.

Please note that even if you don't obtain these exact values, you are expected to achieve results that are close to the provided correct answer. The rest of the answers are too different. However, I realize that it can be important for such specifics to be clarified in the task's explanation. 

Thank you for bringing this to our attention.



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