Research Methods Experiment

Components of Experiments Independent and Dependent variables Pre-testing and post-testing Experimental and control groups Babbie 2005

Independent and dependent variables Treatment or Independent Variable the stimulus, manipulation, or intervention that the researcher creates or delivers to one set of participants or clients. Dependent Variable is the outcome or condition that may change as a result of being subjected to or exposed to the treatment or an independent variable.

Pre-testing and post-testing Pre-test is the measurement of the dependent variable prior to treatment or intervention. Post-test is measurement of the dependent variable after the treatment/ independent variable has been applied.

Experimental and Control groups Must be as similar as possible An Experimental Group are those who receive the treatment or are exposed to the independent variable under study. The Control Group are those who do not receive the treatment or independent variable under study. Copyright @ Allyn & Bacon 2003

Classical Experiment At least two groups (control and experimental) Randomly assign people to groups Treat the experimental group by manipulation the independent variable Observe the effect of the treatment on the dependent variable in the experimental group Compare the dependent variable differences in the experimental and control groups

Diagram of Classical Experimental Design Babbie 2005

Some Notation O1 X O2 O1 O2 Independent variable/Treatment is X Measurement of the dependent variable is notated as O Pre-test is O1 (Observation on the dependent variable at time 1) Post-test O2 (Observation on the dependent variable at time 2) O1 X O2 O1 O2

Relationships Among Pre-Post Designs There are three major types of pre-post program-comparison group designs all sharing the basic design structure shown in the notation above: The Randomized Experimental (RE) Design The Nonequivalent Group (NEGD) Design The Regression-Discontinuity (RD) Design The designs differ in the method by which participants are assigned to the two groups.

The Randomized Experimental (RE) Design In the RE, participants are assigned randomly O1 X O2 O1 O2

The Nonequivalent Group (NEGD) Design In the NEGD, assignment of participants is not explicitly controlled -- they may self select into either group, or other unknown or unspecified factors may determine assignment.

The Regression-Discontinuity (RD) Design In the RD design, they are assigned using a cutoff score on the pretest.

The Solomon Four-Group Design Two of the groups receive the treatment and two do not. Further, two of the groups receive a pretest and two do not O1 X O2 O1 O2 X O2 O2

The Minneapolis Domestic Violence Experiment (1983) Goal was to find the most effective strategy Three groups: two treatment groups and one control Police officers volunteering to take whatever action was dictated by a random system: instruction in an envelope Three different instructions: (1) arrest the suspect; (2) separate or remove the suspect from the scene for 8 hours; (3) advise and mediate

Minneapolis Domestic Violence Experiment Experimental group I Arrest O1 X1 O2 19% Experimental group II Separate X2 33% Control group Mediate 37% Victims have interviewed every two weeks for the next 6 months, police records have been monitored as well Most influential policy experiment Arrest works more effectively in deterring domestic violence

Experiments in Social Science Not always possible (ethical issues) Quasi-experiments or natural experiments Example: Effect of the decision to conduct crackdown on drinking and driving by a local police force (planned interventions) Occasionally, natural events (catastrophe or tornadoes) might substitute planned interventions

Field Experiments Field experiments are used outside the laboratory. But although field experiments overcome the problem of experiments taking place in an unnatural setting, these experiments do have other problems associated with them It is not possible to control variables as closely as it is in the laboratory

Field Experiments Also, in some field experiments, the fact that an experiment is taking place can affect the results, as explained before with the ‘Hawthorne Effect’ To possibly avoid this, it is necessary that the subjects of experimental research are unaware that the experiment is taking place

Field experiment This, however, raises a further problem: the morality of conducting experiments on people without their consent Some sociologists strongly object to do this Although field experiments open up greater possibilities than laboratory experiments, they are still likely to be confined to small-scale studies over short periods of time. Experimentation on society as a whole, or on large groups of society, is only likely to be possible with the consent of governments

Field experiment Few governments are willing to surrender their authority to social researchers who are keen to test the theories and hypotheses they have developed In these circumstances sociologists normally rely upon studying society as it is, rather than trying to manipulate it so that their theories can be tested directly

Strengths Weaknesses In real life, only rarely one variable actually a cause of another one Difficult to test very complex hypotheses (difficult to manipulate and control more than one or two variables) Ethical issues The only method that allows us to test the causal relationships between variables Random assignment of subjects to experimental and control groups allows us to test our hypotheses