1. LECTURE 7 CAUSATION AND DESIGN EPSY 640 Texas A&M University

2. RANDOMIZATION Randomization in the context of the experiment means that each case, element, or member of the sample has an equal chance of being in either experimental or control group. It is crucial to note that this procedure has absolutely nothing to do with sampling from a population.

3. RANDOMIZATION NOTATION GROUP 1RXO GROUP 2RO Denotes randomizedDenotes a treatment or specific condition not in group 2 Denotes an observation or measurement Temporal sequence

4. RANDOMIZATION AND CAUSATION The fundamental concept of randomization is not that various causes that affect a case are eliminated but that they are distributed randomly across the groups initially. That is, an experimental first grade class is not expected to be identical to a control first grade class; the two classes are expected to differ only randomly from each other as a study is initiated if randomization occurred.

5. RANDOMIZATION AND CAUSATION Pearl’s definitions fit because randomization creates genuine causes: Y Z X Z and Y are independent given X

6. RANDOMIZATION AND INTERNAL VALIDITY Campbell and Stanley (1963) presented a list of potential alternative causal arguments for the outcomes of a research study in addition to the hypothesized experimental treatment termed threats to internal validity of an experiment. These threats are not guaranteed to exist in a given study, but they are possible explanations that the researcher either must attempt to account for or acknowledge. Research is a public activity in which the warrants (Phillips, 1994) for a researcher’s conclusions must be made public The force of the researcher’s argument is a major part of the acceptance of the research, both for publication and for incorporation into the thinking in the field of study. The threats are to a varying degree overcome by randomization.

7. INTERNAL VALIDITY THREATS 1X 1 O 1 2X 2 O 2 SELECTIONTESTING MATURATIONHISTORY REGRESSIONMORTALITY INSTRUMENTATIONCOMBINATIONS

8. SELECTION NONRANDOM ASSIGNMENT SO THAT GROUPS ARE DIFFERENT INITIALLY SELF-SELECTION INTO GROUPS In studies of science curricula developed by the National Science Foundation teachers volunteered to teach a new curriculum. In attempting to compare classrooms in which the new curricula were taught with those in which the standard curriculum was taught, the self-selection threat was present. Except in a few randomized studies, most curriculum studies must deal with this self-selection threat.

9. MATURATION DIFFERENTIAL PHYSICAL CHANGE OVER TIME IN TWO GROUPS –SHORT TERM (FATIGUE) –LONG TERM (DEVELOPMENTAL)

10. MATURATION In a study of reading development in first grade children, Tangel and Blachman (1995) compared children who had been in an experimental program in kindergarten and continued that program with children who had not had the experimental kindergarten program. Even though the children were randomized at the start of kindergarten, after a year of differential treatment there is no reason to believe the children are any longer similar (selection threat) or that given the differential reading activities will progress at the same rate (maturation). The better strategy would have been to re-randomize the experimental group into experimental and standard programs.

11. INSTRUMENTATION CHANGE IN MEASUREMENT FROM ONE GROUP TO THE OTHER CHANGE IN MEASUREMENT FROM ONE MEASURING DEVICE (OR PERSON) TO ANOTHER CHANGE IN DEFINITION DURING TREATMENT/INTERVENTION PERIOD

12. INSTRUMENTATION Willson (1979) reported a study of accidents in South Dakota during the 1970’s in which the definition of a reportable accident changed three times. He criticized an alcohol awareness program evaluation that concluded the program decreased accidents based on a drop that coincided with the change in accident reporting.

13. INSTRUMENTATION Willson (1980) reported that, during a period of a year in coding articles for a review, he checked his earlier work. As a result of systematic differences in how elements were coded over time, he had to recode the entire first quarter of the articles to make them consistent with the later coding. He concluded that the process of review had changed his understanding of the elements being coded and that the later work was conceptually superior to the earlier.