## Participate and Analyze Data from a 2 X 2 experiment

Students can participate in this online, 2 X 2 eyewitness testimony experiment.
A data file containing each participant's level on the first independent variable (1= eyewitness is 75% confident, 2=eyewitness is100%) is in the first column, each participant's level on the second independent variable (1= eyewitness has history of assault, 2= eyewitness has history of depression), and each participant's score on the dependent variable (1= sure the defendant is not guilty; 7 = sure that the defendant is guilty) is in the third column and is available from this link.

Data from each participant is separated by the word "endline." Thus, suppose we had data from 4 participants: (a) a participant in the eyewitnesswas75% confident, eyewitness was arrested for assault condition who rated the defendant's guilt as a "3," (b) a participant in the eyewitness was 75% confident, eyewitness was hospitalized for depression condition who rated the defendant's guilt as a "4,"(a) a participant in the eyewitness is 100% confident, eyewitness was arrested for assault condition who rated the defendant's guilt as a "5,"(a) a participant in the eyewitness is 100% confident, eyewitness was hospitalized for depression condition who rated the defendant's guilt as a "6." In that case, the data file from the above link would look like this:
1,1, 3 endline
1,2, 4 endline
2, 1, 5 endline
2, 2, 6 endline

Students can analyze the data by plugging it into the following website. Alternatively, you could have students calculate the means and standard deviations (either by hand or in Excel) for the four cells and then analyze the data using the following applet.

If you want students to see a more sophisticated data file --one that could help screen out people who participated more than once, send them to this file.

If you want to create a data file that contains only your students' data, tell your students to put a certain number (e.g., 8) in the code number box. That number will put your class's data in a separate file. For example, if they all put the number 8 in the box,
their data will be stored in the file http://markwebtest.netfirms.com/data/c11eyewitnessA8.txt
If, on the other hand, they all put the number 66 in the box, their data will be stored in the file
http://markwebtest.netfirms.com/data/c11eyewitnessA66.txt

If you give your class a code number, the data file will contain more than just the participants' levels on the two independent variables and participants' scores on the rating scale. For example, for the three participants mentioned above, the data file might look like this:
0/17/105, 9:19:16, 60.15.41.14, http://markwebtest.netfirms.com/cgi-bin/randassign2X2m.pl, 1,1. 3 endline
0/17/105, 9:20:30, 60.15.41.14, http://markwebtest.netfirms.com/cgi-bin/randassign2X2m.pl, 2,1, 4 endline
0/17/105, 9:21:12, 60.15.41.14, http://markwebtest.netfirms.com/cgi-bin/randassign2X2m.pl, 1,2, 7 endline

Such a data file would tell us that all three scores came from individual(s) who participated in the experiment on the same day (0/17/105 means January 17, 2005), at about the same time (between 9:19 and 9:21), using the same computer (a computer with the IP address of 60.15.41.14), and using the same website
( http://markwebtest.netfirms.com/cgi-bin/randassign2X2m.pl).

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