Question

Question 382 pts

Which of these would be the stronger quasi-experimental design?

Group of answer choices

one-group posttest-only design

posttest-only design with a nonequivalent control group

pretest-posttest design with a nonequivalent control group

one-group pretest-posttest design

Answer 1

Quasi experiment:

Quasi experiments are studies that aim to evaluate interventions but that do not use randomisation. like randomised trials experiments aim to demonstrate causality between an intervention and an outcome. the randomised controlled trial is generally considered to have the highest level of credibility with regard to assessing causality, in a hospital or public setting the intervention often cannot be randomised for one or more reasons

1. ethical considerations
2. and inability to randomised patients
3. and inability to randomise locations
4. a need to intervene quickly .

Ethical considerations typically will not allow the withholding of an intervention that has known efficacy. interventions often cannot be randomised to individual patients for example in studying the effect of an alcohol based hand disinfectant on vancomycin resistant enterococcus Acquisition rates as determined by surveillances culture, it is difficult to randomise the use of disinfectant to individual rooms for individual patients because once disinfected a staff member is unlikely to agree to be decontaminated before he or she sees the next patient nor is an IRB likely to agree to this similarly and education based interventions to decrease VAP cannot be randomised to individual patients

The lack of random assignment is the major weakness of the Quasi experimental study design. associations identified in quality experiments meet some requirements of casualty because the intervention precedes the measurement of the outcome. also their outcome can be demonstrated to vary statistical E with the intervention. Unfortunately, the statistical Association does not imply causal Association especially if the study is poorly designed. does in many quality experiments one is most often left with the question: are there alternative explanations for the Apparent causal Association? If these alternative explanations are credible the evidence is less than convincing.

The methodological principles that most often result in alternative explanations in Quasi experimental studies of infectious diseases include the following;

1. difficulty in controlling for important confounding variables
2. results that are explained by the statistical principle of regression to the maine
3. maturation effects.

In the Social Sciences literature was a experimental studies are divided into 3 study design categories:

1. Quasi experimental study designs that do not use control groups
2. Quasi experimental study designs that use control groups but no pretest
3. Quasi experimental study designs that use control groups and pretests

1 Quasi experimental study designs that do not use control groups:

1. The pretest- posttest design:This is commonly used study design. a single pretest observational measurement(o1) is made and intervention(X) is implemented and a post test measurement(O2) it is made. for example, O1 could be the acquisition rate of VRE as determined by the result of perirectal surveillance cultures, X could be the introduction of use of an alcohol based hand disinfectant and O2 could be the acquisition rate of acquisition of VRE following the intervention. the inclusion of a protest provides some information about what the acquisition rates might have been had the intervention not occurred .
2. The one group pretest-posttest design that uses a Double pretest: the advantage of the study design over design one is the edition of a second pre test measurement prior to the intervention reduces the likelihood that regression to the main maturation or seasonality could explain the observed Association between the intervention and the post test outcome. for example in a study in which use of an alcohol based hand disinfectant lead to lower viari acquisition rates (o3 <O2 and O1)if one study had two three intervention measurements of VR acquisition rates and they were both elevated this would suggest that there was a decreased likelihood that O3 was lower due to confounding variables maturation effects seasonal effects or regression to the main.
3. the one group pretest posttest design that uses a known equivalent dependent variable:

This design involves the inclusion of a known equivalent dependent variable(b) in addition to the primary dependent variable(a) variables A and B should access similar constructs, that is the two measurements should have similar potential causal variables and confounding variables except for the effect of the intervention. If an educational intervention is aimed at encouraging Hospital staff to raise the heads of the patients beds and to follow a mechanical ventilation weaning protocol one should expect to observe a decrease in the incidence of we AP but not in the incidence of UTI.

the advantage of this design is that it demonstrates reproducibility of the association between the intervention and the outcome for example the association is more likely to be casual demonstrates that use of an alcohol based hand disinfectant results in decreased antibiotic resistance rates both when it is first introduced and again when it is reintroduced following and interruption of the intervention. This design is not often used in the study of infectious diseases because of the ethical issues involved in removing a treatment That seems to be efficacious. However epidemiologically it is a better design than those previously outlined.

All the experimental study designs are ubiquitous in the infectious disease literature particularly in the area of interventions aimed at decreasing the spread of antibiotic-resistant bacteria, little has been written about the benefits and limitations of the experimental approach. As we have outlined a hierarchy of Quasi experimental study designs exist with some designs being more likely than others to permit causal interpretations of observed associations. strengths and limitations of a particular study design should be discussed when presenting data collected in a Quasi experimental study. investigators should choose the strong design that is feasible given the particular circumstances.