Stat 2000: Tips for Web Assign HW 06
Published: Mon, 03/14/11
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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.
If you are taking the course by distance/online (Section D01) click here to see your tips for HW 06.
Study Lessons 7 and 8 up to the start of question 1 in my book at least, if you have it, to prepare for this assignment. You don't really need to learn any of the chi-square stuff in Lesson 8 yet, that is obviously coming in the next assignment, but you do want to learn about joint and marginal proportions to help with question 5 in this assignment. Note, only my new edition of my book discusses joint and marginal proportions in any detail. If you do not have the current edition of my Basic Stats 2 book, I strongly recommend you purchase Volume 2 because the changes have been vast and are addressing changes the course has undergone in the last few years.
Questions 1 to 4 are Lesson 7 stuff, and I am confident you will have no problem doing them once you study Lesson 7. You may want to review how to interpret a confidence interval in Lesson 1 of my book (remember, though, that these are confidence intervals for proportions or the difference between proportions, not means), and review how to interpret a P-value in Lesson 2 of my book (again keeping in mind you are hypothesizing about proportions, not means). Note that, by LCL and UCL, they mean, respectively, Lower Confidence Limit and Upper Confidence Limit. Which is to say, they want the lower and upper limits of your confidence interval.
Question 2(b) requires an alpha/beta table. Re-read the section called "Errors in Hypothesis Testing Revisited" in Lesson 6 (only in the latest edition of my Stats 2 book, volume 1). Of course, you will use a p-hat bell curve, as taught in Lesson 7, to find the appropriate probability.
Question 5 of the assignment applies to Lesson 8 in my book (you need only study to the end of question 4; the remainder of Lesson 8 is covered in your next assignment).
In question 5, the joint distribution is simply the joint proportions found by dividing the appropriate cell count by the Grand Total, and the marginal distribution is the marginal proportions found by dividing the appropriate row or column total by the Grand Total. I discuss this in more detail at the start of Lesson 8 in my new edition only.
Study Lesson 9 to review the principles of Linear Regression in my study book then Study Lesson 10 at least up to the end of question 3 to prepare for this assignment. You do not need to study the section on Multiple Linear Regression at this time. Note that HW 6, 7 and 8 will all deal with concepts from Lesson 10.
Question 1 is just an algebra problem, they have given you a value for x, y and the slope and you can use that to compute the intercept. Note, they have written out the least-squares regression equation for you, and all you have to do is enter the values for the intercept and slope into the boxes.
Question 2 gives you all the info you need to compute the confidence intervals for the slope. I give you the appropriate formula in Lesson 10.
You will use JMP for question 3. Open a "New Data Table" and create three columns. Name the first column "Sex", the second column "Speed", and the third column "Stride rate". Remember, to create a new column, simply double-click in the space at the top of the column, to the right of a pre-existing column. Enter in your data, typing "female" or "male" as appropriate in the "Sex" column. Obviously, enter in all the female data first, then all the male data. Now, on the left of the spreadsheet where it numbers all the rows, click and drag to select all the rows that have "female" scores Now select "Rows" and "Markers" and choose whatever marker you want to represent the females. Now, click and drag to select the "male" rows and select a marker to use for them. Click in the top left corner of the spreadsheet (right above row 1) to deselect the rows and we are now ready to analyze the data.
Question 3(a) and (b): Select "Analyze" then "Fit Y by X". They never make it clear which is x and which is y in this problem, but it appears they want x to be speed and y to be stride rate, so select "Stride rate" and click "Y, Response" and select "Speed" and click "X, Factor". Click OK. You will now see a scatterplot with the two different markers plotted distinguishing the female and male scores. Click the red triangle next to "Bivariate Fit ..." and select "Fit Line" to have JMP compute and graph the least-squares regression line. Select and copy the printout and paste into a file ready for upload.
Question 3(c): Click the red triangle next to "Linear Fit" and select "Save Residuals". JMP will now add a fourth column to your spread sheet called "Residuals Stride rate". Select and copy the entire data table (or just the residuals column) and paste into your file ready for upload. They do not make it clear whether they actually want you to include the residuals in your upload, but why ask you to compute them then?
Question 3(d): Click the red triangle next to "Linear Fit" and select "PlotResiduals". I have no idea what they are getting at in this question. You would expect to see some obvious pattern like the males tend to have positive residuals and the females have negative residuals, or something that makes the females look different from the males, but good luck seeing anything here.
Question 3(e): JMP already did this test for you when you selected "Fit Line". The ANOVA table and the "Parameter Estimates" for the "Stride rate" are giving you all the info you need, but be sure to write out your hypotheses and conclusion in the file you are uploading. You can determine if there is a linear relationship by either testing the hypothesis about zero correlation or a hypothesis about zero slope. JMP gives us the latter in the ANOVA and Parameter Estimates, so I would do the zero slope hypothesis. I show you how to read these outputs in my question 3 of Lesson 10.
Question 4(a): Copy and paste your data into a "New Data Table" being sure to select "Edit" and "Paste with column names" if you are using JMP 8. Select "Analyze" then "Distribution", highlight both columns and click "Y, Columns" then click OK. The "Moments" give you the means and standard deviations they request.
Question 4(b): Select "Analyze" then "Fit Y by X". Assign x and y as they have indicated in part (a). Click OK. Click the red triangle next to "Bivariate Fit ..." and select "Fit Line" to have JMP compute and graph the least-squares regression line. You will see the least-squares regression equation directly below "Linear Fit". I assume they want the t statistic for the correlation which is also the t statistic for the slope which you can read off the "Parameter Estimates" (See my question 3 in Lesson 10 for how to read the printouts.) Note, JMP gives us the coefficient of determination, r-squared which we can easily change into r. Remember, r always has the same sign as the slope.
Question 5: Use the same approach used in question 4 to get all the info they request. Make sure you think about which is x and which is y in this problem. Remember my tips about that in Lesson 9, question 1(a). Note, you will use the "Parameter Estimates" to get the slope and its standard error, but then finish computing the confidence interval yourself.