Quasi Experiments PDF

Chapter 13: Quasi Experiments - Quasi Experiment= A study similar to an experiment except that the researchers do not have full experimental control (e.g., they may not be able to randomly assign participants to the independent variable conditions) - Start by selecting IV and...

Chapter 13: Quasi Experiments - Quasi Experiment= A study similar to an experiment except that the researchers do not have full experimental control (e.g., they may not be able to randomly assign participants to the independent variable conditions) - Start by selecting IV and DV - researchers might not be able to randomly assign participants to one level or the other; they are assigned by teachers, political regulations, acts of nature—or even by their own choice - Examples of Quasi-Experiments - Ex 1: Organ donation - Opt in method (people have to choose yes) vs opt out method (people must go out of way to say no) - These are called default options - People accept default because its effortless, and seems socially ok - 100% in consumed consent countries, much lower everywhere else - nonequivalent control group interrupted time-series design= A quasi-experiment with two or more groups in which participants have not been randomly assigned to groups; participants are measured repeatedly on a dependent variable before, during, and after the “interruption” caused by some event, and the presence or timing of the interrupting event differs among the groups - Ex 2: cosmetic surgery - Does cosmetic surgery really improve self esteem - Researchers cant ethically do this experimentally - Used 600 people who already had chosen to get surgery, and 250 who had originally wanted to but didn't - Looks experimental, but because of no random assignment its not - Asked people questions before and after surgery about happiness - nonequivalent control group pretest/posttest design - Ex 3: shows and suicide - Wanted to see effect of 13 reasons why - Looked at shows most popular time and examined suicide rates then - interrupted time-series design= participants are measured repeatedly on a dependent variable before, during, and after the “interruption” caused by some event, and the presence or timing of the interrupting event differs among the group - main concern is internal validity - Internal validity= the ability to draw causal conclusions from the results - Researchers do not have full control of the independent variable in a quasi-experiment - Threats to validity - Selection effects - relevant only for independent-groups designs - selection threat to internal validity applies when the kinds of participants at one level of the independent variable are systematically different from those at the other level - Design confounds - ,some outside variable accidentally and systematically varies with the levels of the targeted independent variable - Maturation threat - occurs when, in an experimental or quasi-experimental design with a pretest and posttest, an observed change could have emerged more or less spontaneously over time - History threat - occurs when an external, historical event happens for everyone in a study at the same time as the treatment - With a history threat, it is unclear whether the outcome is caused by the treatment or by the external event or factor. - Regression to the mean - occurs when an extreme outcome is caused by a combination of random factors that are unlikely to happen in the same combination again, so the extreme outcome gets less extreme over time - regression to the mean can threaten internal validity only for pretest/posttest designs - Attrition threat - attrition occurs when people drop out of a study over time - an internal validity threat when systematic kinds of people drop out of a study - Testing and instrument threats - testing threat is a kind of order effect in which participants tend to change as a result of having been tested before - A measuring instrument could change over repeated uses, and this change would threaten internal validity - Observer bias - you simply ask who measured the behaviors. Was the design blind (masked) or double-blind? For experimental demand, you can think about whether the participants were able to detect the study’s goals and respond accordingly - Demand characteristics - when participants guess what the study is about and change their behavior in the expected direction  - Placebo effect - when participants improve, but only because they believe they are receiving an effective treatment - Balancing priorities - Real world opportunities - they present real-world opportunities for studying interesting phenomena and important events - External validity - can enhance external validity because of the likelihood that the patterns observed will generalize to other circumstances and other individuals - Ethics - Many questions of interest to researchers would be unethical to study in a true experiment - experiments can be an ethical option for studying these interesting question - Construct validity - To test validity, , you would interrogate how successfully the study manipulated or measured its variable - quasi-experiments show excellent construct validity for the quasi-independent variable - STATISTICAL VALIDITY - ask how large the group differences were estimated to be (the effect size). - Quasi-Experiments and Correlational Studies - quasi-experiments seem similar in design to correlational studies - in quasi-experiments the researchers tend to select their samples more intentionally than they do in most correlational designs - In correlational studies, researchers select a sample (such as a large survey sample, as in the Cacioppo study), measure two variables, and test the relationship between them - Quasi-Independent Variables Compared with Participant Variables - participant variable= categorical variable, such as age, gender, or ethnicity, whose levels are measured rather than manipulated - Studies with participant variables are intended to document similarities and differences due to social identities - , quasi-independent variables focus less on individual differences and more on potential interventions such as laws, media exposure, or education