Stat 1000: Tips for Web Assign HW 10
Published: Thu, 03/17/11
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General Tips for Web Assign and JMP
When working with Web Assign, always enter the answer to one specific box and then click "Submit Answer" to confirm that is correct before you move on to another box. Do not enter several answers all at once in several boxes before you click "Submit Answer". You risk being marked wrong due to some typo or something.
For some strange reason, JMP 8 occasionally computes wrong answers even if you have copied and pasted your data correctly. I suggest that, if it is feasible, type the given data into your calculator (in Stat mode as shown in Appendix D of my book), and have your calculator compute the sample mean. Compare that answer with JMP's answer for the sample mean. If they are the same, everything is fine. If they are not the same, close JMP 8 and restart it, recopy and paste the data, and check again. Sometimes you have to do this 2 or 3 times before JMP finally works. If it is not feasible to use your calculator to compute the sample mean, have JMP do the question 2 or 3 times, being sure to restart JMP and recopy the data each time, and confirm that JMP gives you the same answer each time before risking entering the results into Web Assign.
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Study Lesson 9 in my book, if you have it, to prepare for this topic.
First, be sure to note
whether a question gives you σ, the population standard deviation, or s, the
sample standard deviation. That dictates whether you will use z or t when
testing your hypothesis. I would assume, at this stage, you are likely
to be given σ most of the time.
Question 1 is basic P-value stuff as taught in Lesson 9.
Questions 2 and 3 are a good run through of the 5 steps to test a hypothesis.
Question 4:
If you need to use JMP or Crunchit! to make a confidence interval. Personally, I would use JMP. Select and copy the data. Click "New Data Table", then select "Edit" then "Paste with Column Names". Now select "Analyze", "Distribution" and highlight "radon" and click "Y, Columns", then click OK. You are now looking at a histogram and stuff. Click the red triangle next to "radon" then select "Confidence Interval" from the drop-down list. Select "Other" to get a pop-up menu. It probably already has 0.95 typed in (for 95% confidence interval), but, if not, be sure to type in 0.95. Make sure you click the box saying "Use known Sigma". Click "OK" and you will then get a pop-up menu to type in the sigma value. I believe σ = 9 in your case. Click "OK" and JMP gives you the Confidence Interval at the bottom of the printout.
If you want to use Crunchit! Copy the "http:..." stuff for the link to the data (shown at the top in your web browser) then select "Data" and "Load Data from URL". Paste the link into the box and make sure the box saying "use first line as column names" is selected. Make sure you also click the drop-down menu next to "Delimiter" and select "whitespace". Now, you should see the data given in two columns in your spreadsheet. Select "Statistics", then select "Z tests", then select "One-sample". In the pop-up window, make sure you click "radon" in the "Variable" box to highlight it. Type the given standard deviation into the box (again, σ = 9) and make sure the slider is set at 95% confidence and click "OK". You now get a printout showing, among other things, the 95% CI.
If you need to use JMP or Crunchit! to test a hypothesis. You should already be in the output screen having done the confidence interval in part (a). You are now looking at a histogram and stuff. Click the red triangle next
to the variable and select "Test Mean" from the drop-down list. Enter in the
mean from your null hypothesis and enter in the given standard deviation. Click
"OK" and JMP gives you the hypothesis test at the bottom of the printout. Look
at my questions 13 and 14 for examples of how to read this printout.
If you want to use Crunchit! You should already have the data pasted in from part (a).
Select "Statistics", then select "Z tests", then select "One-sample". In the pop-up window, make sure you click the appropriate variable ("radon") in
the "Variable" box to highlight it. Type the given standard deviation
into the box and type in the mean you are using in your null hypothesis. Be
sure you click whether you are doing a two-sided, upper-tailed (greater than) or
lower-tailed test (less than) or else you will not be given the correct
P-value. Click "OK". You now get a printout showing, among other things, the
test statistic and P-value.
In either case (JMP or Crunchit!), you can now select, copy and paste your
output to a file ready for upload as usual.
Question 5:
Follow the same steps as done in question 4 to test the hypothesis about IQ.
Make sure you read my section on P-values to learn how to properly
interpret your P-value.
In question 6 in the Web Assign assignments remember the
note I write after my question 4 talking about statistical significance versus
practical significance. Also, remember the Law of Large Numbers taught in
Lesson 7 of my book.