Experimental and Quasi-experimental Method

September 16,2008

Learning Objectives

• Review APA reference list• Gain some experience with

experimental/quasi-experimental designs.• Learn how to use excel to analyze

experimental data.• Continue with introduction to writing a

scientific paper.

ReferencesReferences

Brown, W. M., & Moore, C. (2002) Fluctuating asymmetry and romantic jealousy. Evolution and Human Behavior, 24, 113-117.

Buss, D. M. & Greiling, H. (1999). Adaptive individual differences. Journal of Personality, 67(2), 209-243.

Buss, D. M. (1991). Evolutionary personality psychology. Annual Review of Psychology, 42, 459-491.

Buss, D. M. (1997). Evolutionary foundations of personality. In Hogan, R., (Ed.), Handbook of personality psychology (pp. 317-344). London: Academic Press.

Buss, D. M. (2000). The dangerous passion: Why jealousy is as necessary as love and sex. New York: Free Press.

First Data Collection

• This time you will be the participants.• We are going to run a quasi-experiment • For now you do not need to know what are

the conditions of the quasi-experiment.

Instructions

• Go to http://www.thewritingpot.com/stroop/

Instructions

• Go to http://www.thewritingpot.com/stroop/• There are going to be a series of colored

words.

Instructions

• Go to http://www.thewritingpot.com/stroop/• There are going to be a series of colored

words.• Your task is to hit the key which corresponds

to the color of the word not what it says.

Instructions

• Go to http://www.thewritingpot.com/stroop/• There are going to be a series of colored

words.• Your task is to hit the key which corresponds

to the color of the word not what it says.• If you are ready go ahead and click on try

experiment and then hit space bar.

Stroop Effect Continued

• When you are done write down click on view results.

• Write down the average time for words which were different for the color and the amount of time it took for words which matched the color.

• Now repeat this entire process two more times.

Microsoft Excel

• Open a new database.• Write the following variable names:

congruent1, congruent2, congruent3,averagecongruent, noncongruent1, noncongruent2, noncongruent3, average congruent.

• Enter your scores from the experiment.

Calculating a mean in Excel

• In the cell under average congruent type =average(

• Type a2:c2) or highlight the cells which contain your congruent data.– In both cases you should have something like the

following : =average(a2:c2)

• Do the same for non congruent variables

Were you strooped?

Were you strooped?• First you might want to plot mean stroop effects.– To do this highlight the Average stroop scores for

congruent and non-congruent• In this case the ctrl button is helpful.• First highlight one press control and highlight the other.

– Now click on insert graph– Pick the bar graph– Hit enter

• If your non-congruent stroop average score was higher than the average congruent score you were strooped

Here are my scores

Did your performance improve?

• How would we know?• We could plot the learning curve for each

condition.• First highlight your congruent1, congruent2,

and congruent3 scores.• Now make a similar graph as before.

My Improvement

Was the Class Strooped?

• First we have to enter data. • We already have the variable names in our

database. • I’m going to call each of you one at a time. – I want everyone to enter their classmate’s scores.– I also want them to record each participant’s sex

The Dataset Congruent1

Congruent2

Congruent3

AverageCongruent

Noncongruent1

Noncongrent2

Nongongrent3

Average Congruent

Sex

Let’s Do a T-Test

• On toolbar on top click “Tools” dropdown box will appear – Choose “Data Analysis” then . . .

• Click “t-test: 2 samples assuming equal variance.”

• Highlight data: You should see a box with room to enter numbers for “Variable 1 range” and “Variable 2 range.”

• Hit Enter

Are males more easily strooped?:Our quasi-experiment

• concept is the same – comparing means

• analysis is a bit more complicated• What do we need to do?

Are males more easily strooped?

• concept is the same – comparing means

• analysis is a bit more complicated• What do we need to do?– Hint- What are our independent variables

Data Manipulation

• How do we calculate this difference score?– First type “=(“ in cell J2

• This creates a new variable. • If you want you could name it stroop score.

– Highlight the noncongruent average • (cell H2 if you followed my example)

– Follow that with a – sign– Then Highlight the congruent average

• (cell d2)– The final product should read =(H2-D2)

Data Manipulation

–Now highlight cell J2• There will be a little box on the border of that

cell • Click and drag it down to the end of the data

set.• This will give you the stroop score for each

person.– Positive numbers mean they were strooped

negative or scores of zero means they were not.

Now the Dependant Variable

• We have to sort the data set• We need all the males in one section and all

the female data on the other.• Highlight all the data by clicking on the top left

hand corner of the spreadsheet.• Click on data • Click on sort• Sort by the column for the variable sex.

Let’s Do a T-Test• On toolbar on top click “Tools” dropdown box

will appear – Choose “Data Analysis” then . . .• Click “t-test: 2 samples assuming equal

variance.” • Highlight data: You should see a box with room

to enter numbers for “Variable 1 range” and “Variable 2 range.”– This type highlight the difference scores for one of the

sexes for “variable 1 range” and highlight the difference scores for the other sex “variable 2 range”

• Hit Enter

Assignment

• I want you to write up a methods and results section for the quasi-experiment we just conducted.

• See pages 367 and 368 in the Leary book.