File Name: quasi experiment strengths and weaknesses .zip
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 to treatment or control.
- Quasi-Experimental Design and Methods
- Quasi experiment
- An introduction to quasi-experimental designs
Jump to navigation. The paper provides a brief overview and then provides an outline of when it is appropriate to use and some of the ethical and practical limitations of its use. In both experimental i. A quasi-experimental design by definition lacks random assignment, however.
Quasi-Experimental Design and Methods
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.
Experiments are conducted both in the laboratory and in real life situations. 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 a quasi-experimental research design. In an experiment, the researcher manipulates the factor that is hypothesized to affect the outcome of interest.
The factor that is being manipulated is typically referred to as the treatment or intervention. The researcher may manipulate whether research subjects receive a treatment e.
Suppose, for example, a group of researchers was interested in the causes of maternal employment. They might hypothesize that the provision of government-subsidized child care would promote such employment. They could then design an experiment in which some subjects would be provided the option of government-funded child care subsidies and others would not. The researchers might also manipulate the value of the child care subsidies in order to determine if higher subsidy values might result in different levels of maternal employment.
Traditionally, experimental researchers have used convenience sampling to select study participants. However, as research methods have become more rigorous, and the problems with generalizing from a convenience sample to the larger population have become more apparent, experimental researchers are increasingly turning to random sampling.
In experimental policy research studies, participants are often randomly selected from program administrative databases and randomly assigned to the control or treatment groups.
The two types of validity of experiments are internal and external. It is often difficult to achieve both in social science research experiments. One potential threat to internal validity in experiments occurs when participants either drop out of the study or refuse to participate in the study. If particular types of individuals drop out or refuse to participate more often than individuals with other characteristics, this is called differential attrition.
For example, suppose an experiment was conducted to assess the effects of a new reading curriculum. If the new curriculum was so tough that many of the slowest readers dropped out of school, the school with the new curriculum would experience an increase in the average reading scores.
The reason they experienced an increase in reading scores, however, is because the worst readers left the school, not because the new curriculum improved students' reading skills. For example, a research study shows that a new curriculum improved reading comprehension of third-grade children in Iowa. To assess the study's external validity, you would ask whether this new curriculum would also be effective with third graders in New York or with children in other elementary grades.
It is particularly important in experimental research to follow ethical guidelines. Protecting the health and safety of research subjects is imperative. The National Institutes of Health supplies strict guidelines for project approval. Many of these guidelines are based on the Belmont Report pdf. The environment in which the research takes place can often be carefully controlled. Consequently, it is easier to estimate the true effect of the variable of interest on the outcome of interest.
Experiments and Quasi-Experiments An experiment is a study in which the researcher manipulates the level of some independent variable and then measures the outcome. 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.
Similarities between true and quasi-experiments: Study participants are subjected to some type of treatment or condition Some outcome of interest is measured The researchers test whether differences in this outcome are related to the treatment Differences between true experiments and quasi-experiments: 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.
Thus, the researcher must try to statistically control for as many of these differences as possible Because control is lacking in quasi-experiments, there may be several "rival hypotheses" competing with the experimental manipulation as explanations for observed results Key Components of Experimental Research Design The Manipulation of Predictor Variables In an experiment, the researcher manipulates the factor that is hypothesized to affect the outcome of interest.
Random Assignment Study participants are randomly assigned to different treatment groups All participants have the same chance of being in a given condition Participants are assigned to either the group that receives the treatment, known as the "experimental group" or "treatment group," or to the group which does not receive the treatment, referred to as the "control group" Random assignment neutralizes factors other than the independent and dependent variables, making it possible to directly infer cause and effect Random Sampling Traditionally, experimental researchers have used convenience sampling to select study participants.
Validity of Results The two types of validity of experiments are internal and external. Internal Validity When an experiment is internally valid, we are certain that the independent variable e.
Since research subjects were randomly assigned to the treatment child care subsidies available and control no child care subsidies available groups, the two groups should not have differed at the outset of the study.
If, after the intervention, mothers in the treatment group were more likely to be working, we can assume that the availability of child care subsidies promoted maternal employment One potential threat to internal validity in experiments occurs when participants either drop out of the study or refuse to participate in the study. External Validity External validity is also of particular concern in social science experiments It can be very difficult to generalize experimental results to groups that were not included in the study Studies that randomly select participants from the most diverse and representative populations are more likely to have external validity The use of random sampling techniques makes it easier to generalize the results of studies to other groups For example, a research study shows that a new curriculum improved reading comprehension of third-grade children in Iowa.
Glossary terms related to validity: internal validity external validity differential attrition Ethics It is particularly important in experimental research to follow ethical guidelines.
The basic ethical principles: Respect for persons -- requires that research subjects are not coerced into participating in a study and requires the protection of research subjects who have diminished autonomy Beneficence -- requires that experiments do not harm research subjects, and that researchers minimize the risks for subjects while maximizing the benefits for them Justice -- requires that all forms of differential treatment among research subjects be justified Advantages and Disadvantages of Experimental Design Advantages The environment in which the research takes place can often be carefully controlled.
Disadvantages It is often difficult to assure the external validity of the experiment, due to the frequently nonrandom selection processes and the artificial nature of the experimental context.
While it is a basic, For a scientific investigation to produce reliable results, it must meet all the following criteria: … Public health practice involves implementing or adapting evidence-based interventions into new settings to improve health for individuals and populations. Quasi-experimental research designs, like experimental designs, test causal hypotheses. Of the great strengths of such approaches. Single-Subject Experiments. Experimental design is used to study the cause and effect relationship between variables under study. Table 6.
Metrics details. The last two decades have seen a growing recognition of the need to expand the impact evaluation toolbox from an exclusive focus on randomized controlled trials to including quasi-experimental approaches. This appears to be particularly relevant when evaluation complex health interventions embedded in real-life settings often characterized by multiple research interests, limited researcher control, concurrently implemented policies and interventions, and other internal validity-threatening circumstances. To date, however, most studies described in the literature have employed either an exclusive experimental or an exclusive quasi-experimental approach. This paper presents the case of a study design exploiting the respective advantages of both approaches by combining experimental and quasi-experimental elements to evaluate the impact of a Performance-Based Financing PBF intervention in Burkina Faso.
An introduction to quasi-experimental designs
Each data collection technique has its own set of strengths and weaknesses. Examples of this study:Milgram and Grifiths Baron Cohen Quasi-Experimental Research vs.
While it is a basic, Recent years have seen important advances in the design and analysis of both randomized experiments and quasi-experiments.
quasi experiment strengths and weaknesses pdf
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