Other's On-Line Resources (Chapter 9)


Estimation With r
  • Description:
    This interactive on-line resource allows you to build a 95% confidence interval around a correlation coefficient, with you being able to specify both r and n.

  • What to Do:
    1. Click on the colored title of this on-line resource: "Estimation With r."
    2. Enter, in the "r" box, any number you want for the sample correlation coefficient.
    3. Enter, in the "n" box, any number you want for the sample size.
    4. Click on the gray bar that says "Calculate the Confidence Interval."
    5. On the next screen that pops up, look at the CI that's been built for your situation.
    6. Click on your browser's "Back" button, and then repeat Steps 2-5, varying the values of r and n.

  • Sky Huck's Puzzle Question:
    There are 2 ways to get the CI to extend above r PRECISELY the same extent as it extends below r. Can you demonstrate BOTH of them using this on-line resource?
Is r Significant?
  • Description:
    You'll see several correlation coefficients generated from a real study. In this investigation, people were measured in terms of two variables (isometric strength and job performance), with two different measures taken on each of these variable. The bivariate correlation coefficients are presented in a correlation matrix, with each r tested to see if it was statistically significant.

  • Sky Huck's Question to you:
    What kind of relationship exists between the values of r and p in the correlation matrix? Is it a direct relationship or an indirect relationship?
Comparing 2 Correlations
  • Description:
    This interactive resource allows you to see if there is a statistically significant difference between two correlation coefficients. By exerting control over (1) the size of the difference between the two rs and (2) the sample sizes, you'll be able to see that large sample sizes can turn a small difference into something "significant."

  • What to Do:
    1. Click on the colored title of this on-line resource: "Comparing 2 Correlations."
    2. Make 2 private decisions: (a) your level of significance and (b) whether you want to do a one-tailed test or a two-tailed test.
    3. Enter .50 and .55 as the r values for Samples A and B.
    4. Enter 100 for each sample size.
    5. Click "Calculate" and then look to see if you have a statistically significant finding; this will be the case if the computed p is smaller that the alpha level you selected in Step #2.
    6. If you don't have a significant finding, repeat Steps #4 and #5 again and again (each time increasing each n by 100) until you finally can cross over into "The Wonderful Land of Significance."

  • Sky Huck's Puzzle Question:
    What do you think will happen to the computed value of p if you (1) set each n equal to 100, (2) make the two values of r different by .20, and (3) change the "location" of your two r values on the "correlation continuum" (that extends from -1.00 to +1.00)?

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Schuyler W. Huck
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