Quasi-experimental methods are research designs that that aim to identify the impact of a particular intervention, program or event (a "treatment") by comparing treated units (households, groups, villages, schools, firms, etc.) to control units.
Full Answer
What statistical treatment is used in quasi-experimental research?
Methods used to analyze quasi-experimental data include 2-group tests, regression analysis, and time-series analysis, and they all have specific assumptions, data requirements, strengths, and limitations.
What methods are used in quasi-experimental design?
Common examples of quasi-experimental methods include difference-in-differences, regression discontinuity design, instrumental variables and matching.
When would a quasi-experiment be used?
Quasi-experimental studies encompass a broad range of nonrandomized intervention studies. These designs are frequently used when it is not logistically feasible or not ethical to conduct a randomized, controlled trial—the “gold standard” of causal research design.
Does quasi-experimental study has treatment condition?
Differences between quasi-experiments and true experiments The researcher usually designs the treatment. The researcher often does not have control over the treatment, but instead studies pre-existing groups that received different treatments after the fact. Requires the use of control and treatment groups.
What are the four types of quasi-experimental research?
Quasi-experimental research involves the manipulation of an independent variable without the random assignment of participants to conditions or orders of conditions. Among the important types are nonequivalent groups designs, pretest-posttest, and interrupted time-series designs.
Which of the following must be present in quasi-experimental research?
Quasi-experimental research requires the use of a comparison group. The most effective method for equalizing groups of subjects that are being compared in a study is matching.
What is quasi-experimental research method?
"Quasi-experimental research is similar to experimental research in that there is manipulation of an independent variable. It differs from experimental research because either there is no control group, no random selection, no random assignment, and/or no active manipulation."
What is a quasi-experimental study?
Quasi-experiments are studies that aim to evaluate interventions but that do not use randomization. Similar to randomized trials, quasi-experiments aim to demonstrate causality between an intervention and an outcome.
Why would you use a quasi-experimental design?
The greatest advantages of quasi-experimental studies are that they are less expensive and require fewer resources compared with individual randomized controlled trials (RCTs) or cluster randomized trials.
What is treatment in research?
The treatment is any independent variable manipulated by the experimenters, and its exact form depends on the type of research being performed. In a medical trial, it might be a new drug or therapy. In public policy studies, it could be a new social policy that some receive and not others.
What is a treatment condition in an experiment?
In experimental design, a level of an independent variable or combination of levels of two or more independent variables. For example, in an experiment examining the effects of four different drugs on dreaming, research participants or subjects would receive a different drug in each treatment condition.
Which research needs treatment or condition?
Experimental researchExperimental research on the effectiveness of a treatment requires both a treatment condition and a control condition, which can be a no-treatment control condition, a placebo control condition, or a waitlist control condition. Experimental treatments can also be compared with the best available alternative.
Is it ethical to do a quasi experiment?
Ethical. Sometimes it would be unethical to provide or withhold a treatment on a random basis, so a true experiment is not feasible. In this case, a quasi-experiment can allow you to study the same causal relationship without the ethical issues. The Oregon Health Study is a good example.
Can you use quasi experimental design?
Instead, you can use a quasi-experimental design. Example: Quasi-experimental design. You discover that a few of the psychotherapists in the clinic have decided to try out the new therapy, while others who treat similar patients have chosen to stick with the normal protocol. You can use these pre-existing groups to study the symptom progression ...
What is assignment to treatment?
Assignment to treatment. The researcher randomly assigns subjects to control and treatment groups. Some other, non-random method is used to assign subjects to groups. Control over treatment. The researcher usually designs the treatment and decides which subjects receive it. The researcher often does not have control over the treatment, ...
What is non random method?
Some other, non-random method is used to assign subjects to groups. The researcher usually designs the treatment and decides which subjects receive it. The researcher often does not have control over the treatment, but instead studies pre-existing groups that received different treatments after the fact.
What is natural experiment?
In a natural experiment, an external event or situation (“nature”) results in the random or random-like assignment of subjects to the treatment group.
What is the Oregon Health Study?
The Oregon Health Study is one of the most famous natural experiments. In 2008, the state of Oregon decided to expand enrollment in Medicaid, America’s low-income public health insurance program, to more low-income adults.
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What is a quasi experiment?
A quasi-experiment is an empirical interventional study used to estimate the causal impact of an intervention on target population without random assignment. Quasi-experimental research shares similarities with the traditional experimental design or randomized controlled trial, but it specifically lacks the element of random assignment ...
Why are quasi experiments effective?
Quasi-experiments are also effective because they use the "pre-post testing". This means that there are tests done before any data are collected to see if there are any person confounds or if any participants have certain tendencies. Then the actual experiment is done with post test results recorded.
What is grouping in medical?
Grouping means two or more groups, such as two groups receiving alternative treatments, or a treatment group and a no-treatment group (which may be given a placebo – placebos are more frequently used in medical or physiological experiments). The predicted outcome is the dependent variable, which is the y-variable.
What is random assignment in an experiment?
In an experiment with random assignment, study units have the same chance of being assigned to a given treatment condition. As such, random assignment ensures that both the experimental and control groups are equivalent. In a quasi-experimental design, assignment to a given treatment condition is based on something other than random assignment.
What is external validity?
External validity is the extent to which results obtained from a study sample can be generalized "to" some well-specified population of interest, and "across" subpopulations of people, times, contexts, and methods of study.
What is person by treatment?
" Person-by-treatment " designs are the most common type of quasi experiment design. In this design, the experimenter measures at least one independent variable. Along with measuring one variable, the experimenter will also manipulate a different independent variable. Because there is manipulating and measuring of different independent variables, the research is mostly done in laboratories. An important factor in dealing with person-by-treatment designs are that random assignment will need to be used in order to make sure that the experimenter has complete control over the manipulations that are being done to the study.
Why is internal validity important?
Internal validity is the approximate truth about inferences regarding cause-effect or causal relationships. This is why validity is important for quasi experiments because they are all about causal relationships. It occurs when the experimenter tries to control all variables that could affect the results of the experiment. Statistical regression, history and the participants are all possible threats to internal validity. The question you would want to ask while trying to keep internal validity high is "Are there any other possible reasons for the outcome besides the reason I want it to be?" If so, then internal validity might not be as strong.
What is a quasi experiment?
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.
What is quasi experimental research?
Thus quasi-experimental research is research that resembles experimental research but is not true experimental research. Although the independent variable is manipulated, participants are not randomly assigned to conditions or orders of conditions (Cook & Campbell, 1979). Because the independent variable is manipulated before ...
What is interrupted time series?
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 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 (Cook & Campbell, 1979). Because productivity increased rather quickly after the shortening of the work shifts, and because it remained elevated for many months afterward, the researcher concluded that the shortening of the shifts caused the increase in productivity. Notice that the interrupted time-series design is like a pretest-posttest design in that it includes measurements of the dependent variable both before and after the treatment. It is unlike the pretest-posttest design, however, in that it includes multiple pretest and posttest measurements.
What is a time series?
A time series is a set of measurements taken at intervals over a period of time. 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 is “interrupted” by a treatment.
What is a quasi experiment?
What is a quasi-experiment? A quasi-experiment is a type of research design that attempts to establish a cause-and-effect relationship. The main difference with a true experiment is that the groups are not randomly assigned.
What is the independent variable in an experiment?
For example, in an experiment about the effect of nutrients on crop growth: The independent variable is the amount of nutrients added to the crop field.
What is methodology in research?
Methodology refers to the overarching strategy and rationale of your research project. It involves studying the methods used in your field and the theories or principles behind them, in order to develop an approach that matches your objectives.
What is a method in science?
Methods are the specific tools and procedures you use to collect and analyze data (for example, experiments, surveys, and statistical tests ). In shorter scientific papers, where the aim is to report the findings of a specific study, you might simply describe what you did in a methods section.
What is a sample in research?
A sample is a subset of individuals from a larger population. Sampling means selecting the group that you will actually collect data from in your research. For example, if you are researching the opinions of students in your university, you could survey a sample of 100 students.
What is the difference between reliability and validity?
Reliability and validity are both about how well a method measures something: Reliability refers to the consistency of a measure ( whether the results can be reproduced under the same conditions). Validity refers to the accuracy of a measure (whether the results really do represent what they are supposed to measure).
What are quantitative variables?
Quantitative variables are any variables where the data represent amounts (e.g. height, weight, or age). Categorical variables are any variables where the data represent groups. This includes rankings (e.g. finishing places in a race), classifications (e.g. brands of cereal), and binary outcomes (e.g. coin flips).
What is the difference between a quasi-experiment and a control group?
In a true experiment, participants are randomly assigned to either the treatment or the control group, whereas they are not assigned randomly in a quasi-experiment. In a quasi-experiment, the control and treatment groups differ not only in terms of the experimental treatment they receive, but also in other, often unknown or unknowable, ways.
What is the purpose of both experiments?
The purpose of both is to examine the cause of certain phenomena. True experiments, in which all the important factors that might affect the phenomena of interest are completely controlled, are the preferred design. Often, however, it is not possible or practical to control all the key factors, so it becomes necessary to implement ...
What is an experiment in science?
An experiment is a study in which the researcher manipulates the level of some independent variable and then measures the outcome. Experiments are powerful techniques for evaluating cause-and-effect relationships. Many researchers consider experiments the "gold standard" against which all other research designs should be judged.
What is the gold standard for research?
Many researchers consider experiments the "gold standard" against which all other research designs should be judged. Experiments are conducted both in the laboratory and in real life situations.
What are the two types of experimental design?
Types of Experimental Design. There are two basic types of research design: True experiments. Quasi-experiments. The purpose of both is to examine the cause of certain phenomena. True experiments, in which all the important factors that might affect the phenomena of interest are completely controlled, are the preferred design.
What is the purpose of research design?
There are two basic types of research design: The purpose of both is to examine the cause of certain phenomena. True experiments, in which all the important factors that might affect the phenomena of interest are completely controlled, are the preferred design.
What is the term for the factor that is being manipulated?
The factor that is being manipulated is typically referred to as the treatment or intervention.
Types of Quasi-Experimental Designs
- Many types of quasi-experimental designs exist. Here we explain three of the most common types: nonequivalent groups design, regression discontinuity, and natural experiments.
When to Use Quasi-Experimental Design
- Although true experiments have higherinternal validity, you might choose to use a quasi-experimental design for ethical or practical reasons.
Advantages and Disadvantages
- Quasi-experimental designs have various pros and cons compared to other types of studies. 1. Higher external validitythan most true experiments, because they often involve real-world interventions instead of artificial laboratory settings. 2. Higher internal validity than other non-experimental types of research, because they allow you to better co...