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Researchers evaluate the effects of an assigned intervention on an outcome; the investigators intervene in the study by influencing the exposure of the study subjects.

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Experimental Study

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Observational.

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With the exception of the Experimental study all study designs are...

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cause effect relationships and for evaluating the efficacy of prevention and therapeutic interventions.

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Experimental Studies are the Most Useful for establishing...

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Strongest methodological design. Outcomes are compared bwteen two or more gorups of people reveiving different levels of the intervention.

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Between Group Design

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Used where the outcome in a single group is compared before an dafter the assignment of an intervention.

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Within Group Design

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Individual characteristics that might confound an association are controlled. Still susceptible to confounding from time related factors.

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Important strength Of 'Within Group Design'?

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The intervention is applied to individuals on the group level.

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Community Trial

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When an experimental study is performed in a clinical setting.

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Clinical Trial

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Unplanned type of experimental study where the levels of exposure to a presumed cause differ among a population.

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Natural Experiment

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makes intervention and control groups look as similar as possible, thereby minimizing the potential influence of confounding factors. MOst comon in clinical settings.

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Random Assignment`

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Used in experimental studies to minimize potential bias from the placebo effect.

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Blinding (Blind Study)

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inactive substance or treatment given to satisfy a patients expectation of treament.

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Placebo

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defined as the effect on patient outcomes(improved or worsened) that may occur b/c of the expectation by a patient that a particuluar intervention will have an effect.

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Placebo Effect

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Subjects are blinded, but investigators are aware of who is receiving the active treatment.

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Single Blinded placebo controlled study

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Neither the subject or the investigators know who is receiving the active treatment.

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Double Blind studies

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Not only are thetreament and research approaches kept a secret from the subjects, and investigators, but the analysis are completed away from the investigators.

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Triple Blind Study

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1. Slecting the intervention 2. Assembling the study cohort 3. Measuring baseline variables 4. choosing a comparison group 5. ensuring compliance 6. Selecting the outcome (end point).

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Designing a Randomized Controlled Trial

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Selecting the outcome.

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End point

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begins with the research objective, whether its to prevent or treat disease.

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Selecting the Intervention

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A unblinded, uncontrolled study with typically less than 30 patients.

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Phase I Trial

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Determine the safety of a test in humans. Patients in phase I trials often have advanced diseases and have already tried other options.

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Purpose of a Phase I trial?

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Relatively small (up to 50 people) randomized blinded trials that test tolerability, safe dosage, side effects, and how the body copes with te drug.

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Phase II Trials

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which type of diseases a treatment is effective against, further assesss side effects and how they can be managed.

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Phase II Trials Evaluate?

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are much larger and may involve throusands of patients. Typically involve random assignment.

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Phase III Trials

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The efficacy of a new treatment.

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Phase III Trials are USed to Evaluate?

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Identifying info like name address, telephone, demographic inof, allow the researcher to accomplish certain objectives.

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Measuring Base Line Variables

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Will allow the investigators to make changes if needed. Comliance can be monitored in drug studies by self report, pill counts, and urine and blood tests.

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Measuring Compliance

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become particularly useful in randomized controlled trials when the outcome phenomenon of interest is rare.

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Surrogate Endpoints

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1. Run in design. 2. Factorial Design 3. Randomized matched pairs 4. Group Randomization.

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Four types of Randomized Study Designes

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Useful for minimizing bias associatied with loss to follow up. All subjects in the cohort are placed on a placebo and followed for some period of time.

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Run In Design

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The subjects in the cohort at the time of randomization may no longer reflect the population of interest.

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Limitation of the Run In Design

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Allows investigators to address the efficacy of two interventions in a single cohort of studies. Subjects are randomly assigned to one of four groups. Comparing efficacy.

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Factorial Design

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in primary prevention programs.

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Factorial Design is useful

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Provides more accurate estimates than unmatched ranomization and may involve matching on several potential confounders.

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Randomization of Matched Pairs

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Groups or naturally forming clusters are randomly assigned the intervention.

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Group randomization

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Charged with the protection of research subjects. The establishment of IRBs was because of the Tuskegee Syphilis Study.

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Institutional Review Boards

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Ratified the establishment of institutional Review Boards.

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Public Health Service Act of 1985

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Assessed the natural course of syphilis in untreated black males from Macon County Alabama.

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Tuskegee Syphlilis Study

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1. No informed consent. 2. Diagnostic Spinal taps were lied about as being treatment. 3. The contagious nature of the disease was never made known to families of infected cases. 4. Cases were actively prevented from receiving treatment. 5. Published Statistics from the study were intended to promote fear of the disease in order to provide further support for the study.

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Ethical Issues from the Syphilis Study

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The investigators influence the exposure of the study subjects Two types of experimental trials are Controlled trials Community trials

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What do Experimental studies-Also called intervention studies-Do?

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Controlled trials Community trials

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Two types of experimental trials are

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Random assignment makes intervention and control groups look as similar as possible Chance is the only factor that determines group assignment

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Random assignment

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Concurrent comparison group is allocated by a non-random process Assignment Problems- Not effective at controlling unmeasured confounding variables. Measured confounding variables, however, may be adjusted through analytic methods

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Non-randomized study-Also called convenience sample

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Eliminates conscious bias due to physician or patient selection Averages out unconscious bias due to unknown factors Groups are "alike on average"

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Advantages of randomization:

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Ethical issues Interferes with the doctor-patient relationship

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Disadvantages of randomization:

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For non-drug studies such as those involving behavior changes or surgery, it may be impossible or unethical to blind It may also be problematic to blind in drug studies where a treatment has characteristic side effects

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Problems with blinding

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To identify clinical and public health approaches to solving public health problems (how to prevent or treat)

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Purpose of experimental studies

Epidemiology ch. 8

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