Workshop Statistics
Lab 2

Prelab 1: Introduction 2: Files 3: Two-way Table 4: Numerical Summary 5: Graphical Summary 6: Discussion 7: Thought Questions 8: Simulation 9: Applet 10: Analysis 11: Conclusions 12: Application 13: Simulation 14: Comparisons 15: Summary

Application

Part of the reason the Mythbusters found their study so convincing was what they considered to be a large sample size. In this application you will explore the effect of sample size on the p-value. Suppose instead they had obtained the following two-way table:

	yawn seed	control group	Total
yawned	20	8	28
didn't yawn	48	24	72
Total	68	32	100

(a) Calculate the difference in conditional proportions for this table (seeded minus control, show your work). How does it compare to that of the actual study (larger, smaller, the same)?

 

Also include a segmented bar graph displaying this group comparison. Now you want to create the bar graph directly from the two-way table rather than having the "raw data." Adapt one of the following sets of instructions for this data table.

Click here to display Minitab instructions

OR

Click here to display Excel instructions

 

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Enter the two-way table into Data window. Do not include the row and column totals, but do include descriptive row and column labels.
Choose Graph > Bar Chart Use the pull-down menu to select Values from a table.
Select the Stack option under two-way table. Press OK.
Enter the columns containing the explanatory variable groups in the "Graph variables" box. Click inside and the enter the column contain the row labels in the "Row labels" box.
Press the Chart Options button and then check the “Show Y as Percent” box and then Accumulate “Within categories” at level 1.  Press OK twice.

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Enter the two way table into an Excel spreadsheet, including the row and column labels (but the totals are not necessary).
Use your mouse to select over the labels and the inside of the table:
Then get the chart wizard open. For example, Insert > Chart in Excel 2003 or clicking on the chart icon in the menu bar. In Excel 2007, it's Insert > Columns:
Make sure you get the 100% Stacked Column option
Press Finish and you are done. Note, it's fairly easy to change the background color from grey to white and to reverse the roles of the row and column variables if you want…

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Copy this graph into your report.

(b) How does the difference in conditional proportions and segmented bar graph change for this version of the data?

 

(c) Conjecture (state your intuition, no wrong answer) how you think the p-value for this table will compare to that of the actual study (larger, smaller, the same).