Class Notes (838,403)
SOAN 2120 (390)
Lecture

# October 25.docx

5 Pages
65 Views

School
Department
Sociology and Anthropology
Course
SOAN 2120
Professor
David Walters
Semester
Fall

Description
October 25, 2012 Experimental Designs - independent variable  dependent variable (differences in outcomes between two groups) - equivalent o average scores on the dependent variable and o scores on all other variables which are likely to affect the dependent variable - differences: manipulation - how do we establish the equivalence of two or more groups? o Random number tables o Objective: equal probability of being assigned to the group - Essential: (the groups are equivalent) - Conclusion: manipulation - Even with RA the two (or more) groups will not be exactly equal in all respects. - If the assignment is random, we can use tests of statistical significance (manipulation vs. random variation) - As n increases, individual differences decline - Without random assignment (RA): findings may be attributable to pre- existing differences between groups o What is this called? Selection bias - We could compare pre-test scores (dependent variable measures) before the experiment begins o Significantly different?  “equivalent”  proceed as if random assignment had taken place - What about all other potential confounding variables? - This happens automatically with random assignment Experimental Design Notation - Standard Notation (page 181) o R O1 X O2 o R O3 O4 - X represents an “experimental variable or effect” (the independent variable) - O represents a dependent variable observation. Subscripts (scripts) depict the observation; the exact ordering of the numbering is somewhat unimportant. - This experiment has a pre-test and post-test. - First (the top group) gets the change. - Second group is the controlled group. - The pre-test for the experiment group (O1) - The pre-test for the control group (O3) - Finally, the letter R denotes RA Example Experimental Designs (Many Groups) - Do “gimmick devices” improve drinking times? - Group 1: “drink through a bottle” - 3.9 seconds - Group 2: “regular bong” - 2.9 seconds - Group 3: “bottle bong” - 2.5 seconds - Different levels of the independent variable (different treatments) - This experiment would be diagramed as follows: - R X1 O1 - R X2 O2 - R O3 Notice that in this example, there is no pre-test Does this invalidate any of the findings? Internal Validity Whether the experimental condition (treatment) actually had an effect within the experiment itself. - History o When some event other then the experimental manipulation affects an outcome, or changes respondents o Before/after design o How can we know that the change that occurred as a result of the experimental manipulation, as opposed to all of the other things which respondents experiences between the pre-test and the post- test? - Maturation o Maturation is a subset of history o With the passage of time, people get tired, get bored, get hungry o Children subjected to a pre-test post-test design (before/after design)  Example:  Pretest: play with toys  Treatment: violent cartoon  Post-test: play with toys o Changes due to cartoon? Or maturation factors as the afternoon wears on? - Testing o Subjects are observed (tested) more than once o Early testing influences later testing o Example:  Does exposure to a cartoon will lead to more violent play- behaviour?  Children are viewed through a one-way mirror playing with toys (unobtrusive testing)  Dependent variable: observed number of ‘violent acts’  Even though the ‘testing’ procedure is unobtrusive, they may have become bored with their toys – ‘tested’ before o Measures of “performance” of any sort when measured more than
More Less

Related notes for SOAN 2120
Me

OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Join to view

OR

By registering, I agree to the Terms and Privacy Policies
Just a few more details

So we can recommend you notes for your school.