Evidence for treatment Flashcards
What is the best study design for evaluating evidence for treatment?
Intervention trials (these are a form of analytic studies - sutdies that involve explicit comparisons between groups). They involve active interventions or treatments. The investigator determines the method of selection of the patients and allocates the interventions the patients receive.
List types of intervention study - 2
- RCT - experimental laboratory study or clinical trial
- Cross-over studies
What is a RCT?
they involve the study of two or more groups, iwth one or more treatment groups that receive the treatment(s) under study. The control group receives no treatmetn, a placebo or the standard treatment. A key feature of RCTs is random allocation of patients to the groups. This allows for controlling for confounding variables, reduces the chance for introducing bias and helps ensure groups are comparable for all factors other than the treatment under study. All groups should be followed for the same amount of time.
Advantages - RCT - 4
- Random allocation reduces risk of bias and eliminates confounding variables
- increases the chance that differences between groups result from the treatment given
- very powerful study method
- high standard of evidence
Disadvantages - RCT - 2
- Ethical issues (withholding an effective treatment in the control group may be difficult to justify)
- Expensive
What is an RCT laboratory study?
Experimental animals are used. The researcher controls allocation of animals to the groups and administration of treatments. They are the best evidence for cause or treatment effects but may lack relevance to the clinical world.
What is an RCT clinical trial?
Privately owned animals kept in their normal environment are allocated to treatment groups. There is less control of treatment administration that RCT laboratory studies. However clinical trials are the most relevant evidence for clinical practice.
What is a cross-over study?
An intervention study.
Patients are randomly assigned to one of two treatment groups for the first treatment. They are then followed over time for a given outcome. After a period of time, deemd sufficient to prevent residual effects of the first treatment, they then have the other treatment. The patients are then followed for the same period of time and the outcome assessed.
Advantage - cross-over study
each subject acts as its own control, paired analyses with increased power
Disadvantage - cross-over study
treatment with persistent effect will confound results as they will still have residual effects during the second treatment when administered first.
What do you need to look at to assess the validity of intervention studies?
- clearly define research question?
- random allocation?
- randomisation concealed?
- blinding of allocation?
- groups similar at the start of the trial?
- groups treated equally except for the experimental therapy?
- follow up sufficiently long and complete?
- all patients analysed in the group allocated to?
- sample size and study power?
What 2 factors are necessary to a critical appraisal of intervention studies?
- validity of the intervention study
- importance of the findings published
What does the study power indicate?
the ability of the study to detect a clinically relevant difference between treatment groups. This is particularly important for studies reporting negative results - i.e. no difference between treatment groups.
What is a type 2 error?
the study had insufficient power to detect the differences actually present between the groups
How can you determine the importance of the results? 2
- ) what was the magnitude of the treatment effect? (larger magnitude of effect suggests a greater likelihood of a real treatment effect and additionally supports the presence of a clinically relevant treatment effect).
- ) how precise are the estimates of treatment effects?
