Quasi Experimental 6p5a3m

Quasi Experimental

The prefix quasi means “resembling.” Thus quasi-experimental research is research that

resembles experimental research but is not true experimental research.

Quasi-experiment is simply defined as not a true experiment. Since the main component of a true experiment is randomly assigned groups, this means a quasi-experiment does not have randomly assigned groups.

Quasi-experiments are most likely to be conducted in field settings in which random assignment is difficult or impossible. They are often conducted to evaluate the effectiveness of a treatment—perhaps a type of psychotherapy or an educational intervention.

Nonequivalent group design

is a between-subjects design in which participants have not been randomly assigned to conditions.

Quasi Experiment A time series is a set of measurements taken at intervals over a period of time.

Interrupted Time Series Design

Pre testPost test Design

the

dependent

measured

once

variable before

is the

treatment is implemented and once after it is implemented

For example A researcher who wants to evaluate a new method of teaching fractions to third graders. One way would be to conduct a study with a treatment group consisting of one class of third-grade students

and a control group consisting of another class of third-grade students. This design would be a non-equivalent groups design because the students are not randomly assigned to classes by the researcher, which means there could be important differences between them.

Eg… For example, the parents of higher achieving or more motivated students might have been more likely to request that their children be assigned to Ms. Williams’s class. Or the principal might have assigned

the “troublemakers” to Mr. Jones’s class because he is a stronger disciplinarian.

For example • A researcher who is interested in the effectiveness of an antidrug education program on elementary school students’ attitudes toward illegal drugs. The researcher could measure the attitudes of students at a particular elementary school during one week, implement the antidrug program during the next week, and finally, measure their attitudes again the following week. • The pre test-post test design is much like a within-subjects experiment in

which each participant is tested first under the control condition and then under the treatment condition.

For example • A manufacturing company might measure its workers’ productivity each week for a year. In an interrupted time series-design, a time series like this one is “interrupted” by a treatment. In one classic

example, the treatment was the reduction of the work shifts in a factory from 10 hours to 8 hours. Because productivity increased rather quickly after the shortening of the work shifts,

Benefits • Quasi-experimental research may be more feasible because it often does not have the time

and logistical constraints associated with many true experimental designs. • True experimental designs are sometimes impractical or impossible because the research can only effectively be carried out in natural settings. Experimental research can create artificial situations that do not always represent real-life situations. This is largely due to fact that all other variables are tightly controlled which may not create a fully realistic situation. For this reason, external validity is increased quasi-experimental research. • Reactions of test subjects are more likely to be genuine because it not an artificial research environment.

• It can be very useful in identifying general trends from the results, especially in social science disciplines. • It reduces the difficulty and ethical concerns that may surround the pre-selection and random assignment of test subjects. For example, if examining the effects of cigarette smoking by pregnant women on the fetus, it would be unethical to randomly assign pregnant women to groups. • Matching procedures may be used to help create a reasonable control group, making generalization more feasible. For example, if one group of migraine suffers received a new treatment and a second group did

not receive the treatment, the difference in the pain levels may be attributed to the treatment if the control group is an appropriate comparison group. • The results generated can often be used to reinforce the findings of case studies by conducting research

that may lend itself to statistical analysis. • Quasi-experimental approaches may reduce the time and resources required because extensive prescreening and randomization is not required or utilized.

Limitation • The lack of random assignment into test groups leads to non-equivalent test groups which can limit the generalizability of the results to a larger population. Beside of the lack of randomization and the reduced internal validity, conclusions about causality are less definitive in quasi-experimental designs. • Statistical analyses may not be meaningful due to the lack of randomization and the threats to internal validity. • Pre-existing factors and other influences are not taken into because variables are less controlled in quasiexperimental research. For example, when examining the impact of smoking by pregnant mothers, there may be other factors

such as diet, education, overall health, and access to health care in general that may be playing a role in the outcome. If other variables are not controlled, the researcher can be assured that the treatment was the sole factor causing the outcome. • Human error also plays a key role in the validity of any project as discussed in previous modules.

• The research must adhere to ethical standards in order to be valid.