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1 COMM 301: Empirical Research in Communication Lecture 10 Kwan M

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3 Experiments Experiment –method that allows us to evaluate the influence of some independent variables on some dependent variables –while controlling for other intervening variables
1 COMM 301: Empirical Research in Communication Lecture 10 Kwan M Lee
2 Experiments Things to know by the end of the lecture: –Know advantages and disadvantages of experiments –Know how to achieve experimental control to get causal inference Factors influencing control Specific techniques to ensure control –Know the various experimental designs, in terms of Understand logic behind each design structure, how they look like advantages and disadvantages How to apply
Disadvantages Advantages –Allow causal inference –Replication possible by someone else. Disadvantages –Lack ecological isomorphism –Weak generalizability.
no wash on an exam day  1) no wash is lucky vs. 2) more time spend on reading.
6 Factors influencing the amount of control in experiment Manipulation of independent variable Ensuring group equivalence Control of intervening variables
–Give some assurance that if dependent variable changes, it is due to the independent variable –E.g., default experiment setting Passive observation –Cannot be under control of researcher –Natural setting E.g.,Comparison of two existing classes which have different teaching methods.
–How to insure.  see next slides.
–No guarantee of getting equivalent groups But it usually works. –Can use statistical testing to find out how likely the group is non-equivalent. Comparisons of variables not related to dependent variables.
–Expectation is that the groups will be similar If not, non-equivalent with regard to DVs.
matched on intervening variables) –Constancy matching All participants in all groups kept uniform on the characteristic thought to influence the dependent variable. e.g. holding gender constant: test only males –Pairing Each participant in a group is matched with other participants in other group on the variable(s) thought to affect the dependent variable(s) e.g. for each male (female) in treatment group, there is a male (female) in the control group – i.e., equal # of males and females.
–other factors influencing internal validity (e.g., maturation, attrition.).
new training program at a company.
–Limitation: test sensitization –See Graph in p. 86.
16 Pretest-posttest control group design T: treatment group C: control group R: Random Assignment Pr: Pretest X : Treatment (intervention) - : No treatment (intervention) Po: Posttest
17 Amount of Control – High Control Posttest only control group –Randomized assignment to treatment and control groups for group equivalence –No pre-testing, sacrifice some group equivalence –Attempts to counter test sensitization in pretest posttest control group design
T2; C1 vs. C2; C1 [Pr vs. Po]) –Limitations: Costs, especially in subjects Difficulties in interpreting contradicting results.
19 Solomon four-group design
You can assume that a difference of 5% or more represents some sort of effect or difference beyond random chance Were the four groups equivalent. Why. –Random assignment –Pr1 = Pr2 = Po4 Does the treatment have an effect. –Po1 vs Po3; Po2 vs. Po4; Po1 vs. Pr1 Do you see prestest effects (test sensitization). –Po3 vs. Po4; Po1 vs. Po2; Pr2 vs. Po3.
Random assignment not always possible. Shift to moderate control designs. –Pretest posttest nonequivalent group design –Interrupted and multiple interrupted time series.
–Typically, groups already formed naturally E.g. classes –Ability to make causal inferences weakened. Differences in the posttest may be due to initial differences between the groups. –many possible alternative Hs T:PrxPo C:Pr-Po.
23 Amount of Control – Moderate Control Interrupted time series design –Only a single group available The group must serve as both T and C groups series of pretests, establish baseline measure administer treatment series of posttests –Advantages can handle pretest sensitization (if all pretest scores are similar) and maturation (if there is little change from one test to the next) can test the persistency of the treatment effect Pr1Pr2Pr3Pr4 xPo1Po2Po3Po4 Multiple interrupted time series design Pr1Pr2Pr3Pr4 xPo1Po2Po3Po4 Pr1Pr2Pr3Pr4 Po1Po2Po3Po4
24 Amount of Control – Low Control Experimental designs, low control –At times, circumstances do not allow random assignment nor even moderate control by pretest –Not an experiment in a strict sense –Usually for Exploratory studies Single group post test only design Single group pre-post test design Posttest only nonequivalent control group design