Psych. 280: Statistics in Psychological Research Fall 2004 Computer Assignment 2: Factorial design ANOVAs

due: Mon., 11/29/04

For this assignment, you will collect a single data set with which to conduct a factorial design between- subjects ANOVA (in this case, a two-factor ANOVA). To complete this assignment, you will need to undertake three tasks: (a) collect a data set, (b) conduct appropriate analyses, and (c) write a laboratory paper reporting your study and the results that obtained. Please note that you will be using an alpha level of  = .05 for all of your analyses. While you may conduct your study and complete your analyses in small groups, you must write your laboratory report on your own.

Collect a Data Set

You may work in small groups (no more than six of you may work together in a single group) to collect your data. You will need to design a small study that includes two independent variables, one with two levels (e.g., gender) and another that involves three levels. While technically the term independent variable applies to variables that have been manipulated, the statistical analyses we are working with are appropriate for use with non-manipulated variables. For instance, you might ask men and women (one IV) participants to report the amount of conflict (perhaps using a four point scale, where 1 = not at all, 2 = a little bit, 3 = quite a bit, and 4 = very much) they are currently experiencing with their mother, father, or a same-sex friend using a single question (with participants reporting on conflict in only a single category of relationship). Remember, because we are working statistical analyses for independent groups, you must collect data for each group using a different sample of subjects. You must collect data from at least 8 participants for each of the levels of your independent variable.

Conduct Appropriate Analyses

To conduct these analyses, you will first need to enter the data that you collected for your study. Using the SPSS Data Editor window, define two columns for your independent variables and one column for your dependent variable. Remember, you will need to define your independent and dependent variables. To do this, click on the “variable view” icon at the bottom of the SPSS Data Editor window. Type in an eight character label in the “name” column for each of your two variables.

Here is an example of what your data might look like for your first 10 participants: Notice that you can use the values 1, 2, and 3 to represent the three levels of your first independent variable, labeled “relation” (representing ratings of conflict with mother, father, and best-friend, respectively) and values of 1 and 2 to represent the two levels of your second independent variable, labeled “gender” (in this case, men and women, respectively) regardless of the nature of your independent variable. It will be useful to assign labels for these three values. To do this, click on the box in the “values” column in the row for your independent variable; a grey box will appear. Click on the grey box, and a new window will appear:

To enter values, simply type in a numerical value in the “Value” box (e.g., “1”), and then click on the Value Label box to enter a label (e.g., “Maternal relationship”). You must remember to click on “Add” after entering this information for each of the three levels of your independent variable; you may then flick on “OK” to return to the SPSS Data Editor window. Once your data have been entered into the SPSS Data Editor window, be sure to save the file so that you may return to it in the future if this becomes necessary.

To complete the factorial design ANOVA, click on the “Analyze” icon at the top of the window to get the available options, and then select the “General Linear Model” and then the “Univariate” option. Your window look like this: Select the independent variables in the left dialogue box, and then click on the icon to enter them in the “Fixed Factor(s)” box. Then click on “Options”, and you will get a dialogue box that looks like this:

You want SPSS to display all of the means for your study, so select “Overall”, and the other three variables in the window labeled “Factor(s) and Factor Interactions”, and then click on the icon to enter them in the “Display Means for” box. Then click on the “Continue” icon. You may now click on the “OK” icon to conduct the analysis. You will then get an Output window that includes the following information: SPSS provides you with information about the number of participants in each level of each independent variable, and with a summary ANOVA table. You will probably notice that the summary table gives you information about sources of sums of squares with which you are not familiar, and we will not be concerned with some of these sources for this laboratory exercise (e.g., in the rows labeled “Corrected Model”, “Intercept”, and “Total”). The row labeled “RELATION” provides the sum of squares, degrees of freedom, mean square, F-value, and p-value associated with the main effect for this variable. Similar information is provided for the main effect for the other independent variable (in the row labeled “GENDER”), while the information for the interaction between these two variables is reported in the row labeled “RELATION * GENDER”. The values associated with what we have discussed as SSTotal, dfTotal, etc., are reported in the row labeled “Corrected Total”. You will use the mean square error when you conduct your post hoc analyses using Tukey’s HSD test (HINT: when comparing all of the possible differences between group means, k = 6).

SPSS will also display the means for all of your comparisons; this information is in your output window, and will look like this: In the table labeled “RELATION”, SPSS reports the means for each of the levels of the “relation” independent variable, collapsed across gender; the converse is true for the table labeled “GENDER”. The mean for each of the six cells of the 3 X 2 design are reported in the table labeled “RELATION * GENDER”.

Please not that you will need to compute Tukey’s HSD value by hand; SPSS will not compute the appropriate value to use in your analyses, although it will conduct a Tukey’s HSD test.

Write a Laboratory Paper

Your paper should have the following headings:

METHOD Participants

Procedure

RESULTS Two-Factor ANOVA In the Methods section, you will provide a brief description of your sample, including the range of ages represented. You should also briefly describe the procedure you employed to collect your data. Do not say that your sample was “randomly selected” unless you used a random number table to select participants from the phone book. In your Results section, be sure to report your results using APA format discussed on p. 500. Be sure to provide effect size estimates, and to report the results of your post hoc analyses. In addition, provide a table reporting the descriptive statistics for your study (as illustrated on p. 500 of our textbook) and a figure depicting the means for each of the cells in your design. (NOTE: to obtain the standard deviations for each of your cells, simply click on the “Descriptive Statistics” option in the “Options” window in your analysis when you are requesting the various means). You will not have a Discussion section for this laboratory report.

Note: When reporting statistically significant results, write that p < .05, rather than the exact p-value provided in the SPSS printout (although this is not what the textbook instructs you to do).

Important details (provided by Professor Borton):  You should italicize M, SD, t, and p.  When p > .05, report that the difference was NONsignificant, not INsignificant.  Correct way to report nonsignificant differences: t(31) = .38, n.s.  Round everything to 2 decimal places.  The word “data” is plural, hence, “The data WERE collected,” NOT “The data WAS collected.”  Unless you used a random number table or otherwise ensured random selection, you cannot say that you “randomly” chose participants.  Use “men” and “women,” rather than “males” and “females” when talking about human subjects.  Don’t use the word “condition” unless you conducted an experiment and manipulated something.  Typing instructions: You can get the  symbol by typing an “m” in symbol font. Similarly, a  is an s in symbol font. You can get subscripts (and superscripts) by going under the “Format” menu in

Microsoft Word and choosing “Font.” Highlight the letter or number and click on subscript (e.g.,) or superscript (e.g., t2).