McCroskey Scenario t-test Take the McCroskey test yourself to see your apprehension level This...

McCroskey Scenario t-test

Take the McCroskey test yourself to see your apprehension level

This PowerPoint will walk through the comparison of means of the pre and post-tests


Remember the Types of Scales?

Nominal Data (Chi-square) classification data, e.g. m/f no ordering, e.g. it makes no sense to state that M > F arbitrary labels, e.g., m/f, 0/1, etc Ordinal Data (t-test) ordered but differences between values are not important e.g., political parties on left to right spectrum given labels 0, 1, 2 e.g., Likert scales, rank on a scale of 1..5 your degree of satisfaction e.g., restaurant ratings Interval Data ordered, constant scale, but no natural zero differences make sense, but ratios do not (e.g., 30°-20°=20°-10°, but

20°/10° is not twice as hot! e.g., temperature (C,F), dates Ratio Data ordered, constant scale, natural zero e.g., height, weight, age, length Quoted from

http://www.stat.sfu.ca/~cschwarz/Stat-301/Handouts/node5.html


Take McCroskey's PRCA. http://ww3.llcc.edu/speechsurvey/survey.aspx OR http://www.jamescmccroskey.com/measures/prca24.htm

Photo Source http://2.bp.blogspot.com/_27z_ybX1fcc/SafUfnpKgwI/AAAAAAAAAI4/nwRnSJx33dw/s400/speakerbestself.jpg


Study

Imagine that a group of 20 students enrolled in Dr. Cohn's public speaking course. These students took McCroskey's test on the first day of their public speaking course. Scores can range from 24-120, and a score above 65 suggests higher than average apprehension. Dr. Cohn is concerned that she has so many apprehensive students in the class. Here are their scores:

After one term of instruction, Dr. Cohn administered the test at the end of the course because she wanted to see if taking the course lowered student apprehension.

In this case, there is a pre-post test for one group and the data on a scale. Dr. Cohn asks you to calculate the results using a t-test.

Is there a significant difference in the communication apprehension level of the class members before and after taking Dr. Cohn's course?


First, you enter the data.


Pull down “Help,” select “Statistics Coach” if you need help.


Compare means of the pre and post test.


Select two


Related data


Normal Distribution


The “Statistics Coach” help function guides you in what statistical test to use.


What are the means to be compared? The average of the pretest, the average of the posttest. The calculator will figure this automatically as part of the t-test calculation.

Add the 20 scores from the pretest = 1600

Divide by 20 students in the class = 80 is the average or mean for the pretest.

Add the 20 scores from the posttest = 1193

Divide by 20 students in the class = 51


95% confident that the difference is not by chance


Enter Data


From menu

Select “Analyze” Select “Compare Means,” which is

what a t-test does. Select “Paired-Samples T Test,”

which is what the Statistics Coach told us to do based on our answers to the various questions.


If you don’t have SPSS, here is a calculator: http://www.physics.csbsju.edu/stats/t-test_bulk_form.html


The standard deviation helps the researcher determine how much distance from the mean is typical and how much is considered significant.


Using unpaired t-testt= 4.46 sdev= 20.2 degrees of freedom = 38 The probability of this result, assuming the null hypothesis, is less than .0001

Scores are significantly lower after the course. (Remember, this is fictional research.)

We can feel confident that completing the public speaking course helped lower student communication apprehension.


Hope you enjoyed this application practice!

McCroskey Scenario t-test Take the McCroskey test yourself to see your apprehension level This...

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