5. Overview of Study Designs and Experimental Study Designs Flashcards
What are the 6 differences in how study designs differ?
- Number of observations made
- Directionality of exposure
- Data collection methods
- Timing of data collection
- Unit of observation
- Availability of subjects
What is an experimental design study approach?
Manipulation of the study factor - if the exposure of interest was controlled by the investigator
What are the 2 types of design study?
Experimental and Observational
What is an observational design study approach?
Randomization of study subjects - if there was use of random processes to determine exposure of study subjects
What does controlled assignment mean related to in study designs?
Experimental studies/manipulated
What does uncontrolled assignment mean related to study design?
Observational studies
Is a cohort study prospective or retrospective?
Prospective
Is a case control study prospective or retrospective?
Retrospective
Associations between exposure and disease status
slide 10
What does the specific interpretation of results from a 2x2 study depend upon?
the design of the study
How cases status and exposure status were ascertained
Whether cases are incident or prevalent
What are true experimental studies?
They are most convincing for conferring evidence of associations between risk factors and outcomes
for manipulation of study factors and randomization of subjects
What is an example of a true experimental study?
randomized clinical trials
What are the two main types of experimental studies?
- Randomized clinical trials
2. Quasi-experimental studies
What do randomized clinical trials mostly focus on?
individuals
What do Quasi-experimental studies mostly focus on?
on the group or community
What gives the strongest evidence for causality?
Study Designs
specifically with internal validity = experimental studies
What is the strength of the evidence usually referred to as?
internal validity
Will clinical trials generally be representative of a population?
not generally
What does randomization create?
It creates comparable groups by equally distributing known and unknown factors (e.g., confounders) that could otherwise bias results
What is performed after informed consent?
randomization
What are the 3 types of randomization?
- Simple
- Restricted
- Stratified
What does randomization increase?
increases internal validity
What is internal validity?
The ability to make causal inferences from the study results
What is external validity?
The ability to generalize the results to a greater population
What does RCT stand for?
Random Clinical Trial
How do large RCT’s relate to internal or external validity?
large RCT’s generally have good internal validity but poor external validity
What gets to the tension between epi as an science and an applied field of research?
internal vs. external validity
In an external validity RCT when would you compare the study population? and why?
in the latter stages because there is not enough information in the early stages to assess differences in participants vs. non-participants
What is the definition of a Randomized Clinical Trial (RCT)?
A research activity that involves the administration of a test regiment to humans to evaluate its efficacy and safety
What is the variation of usage in RTCs?
there is a wide variation of usage
what was the first use of the term RCT?
the first use of the term was for studies in humans without any control treatment
What does the usage of RCT’s now denote?
a rigorously designed and executed experiment involving random allocation of test and control treatment
What are the 5 characteristics of clinical trials?
- carefully designed and rigidly enforced protocol
- tightly controlled in terms of eligibility, delivery of the intervention, and monitoring of outcomes
- duration ranges from days to years
- participation is generally restricted to a highly selected group of individuals
- Once subjects agree to participate, they are randomly assigned to one of the study groups
What is randomized assignments in design studies?
a method of choice for assigning subject to the treatment or control conditions of a clinical trial
What how might non-randomization confuse assignments in design studies?
non-randomization assignments may cause mixing of the effects of the intervention with difference (like demographics) among the participants of the trial
What is a crossover designs?
any change of treatment for a patient in a clinical trial involving a switch of study treatment
What happens in planned crossover designs?
in planned crossovers a protocol is developed in advance, and the patient may serve as his or her own control
why do unplanned crossover designs exist?
unplanned crossovers exist for various reasons, such as a patient’s request to change treatment
History of clinical trials
slides 28-29
What is a prophylactic trial?
it evaluates the effectiveness of a substance that is used to prevent disease, it can also involve a prevention program
What is a therapeutic trial?
involves a study of curative drugs or a new surgical procedure to improve a patients health
What is the main difference between prophylactic and therapeutic trials?
outcomes
What are clinical trial outcomes referred to as?
clinical outcomes or end points
What could clinical outcomes include?
rates of disease, death, or recovery
How is an outcome of interest measured?
measured both in the intervention and control arms of a trial to evaluate efficacy
these must be measured in a comparable manner!
What is the purpose of blinding (or masking) in clinical trials?
to maintain the integrity of a study and reduce the potential for bias
What are the 2 popular approaches to blinding (or masking) in clinical trials?
- Single blind design - where the subject is unaware of group assignment
- Double blind design - where neither the subject nor experimenter is aware of group assignment
What must happen before a vaccine, drug, or treatment can be licensed for general use?
It must go through several stages of development
Why are there phases to clinical trials?
to protect the public from a potentially deleterious vaccine
to satisfy the urgent needs for new vaccines
What are the 2 primary stages in the development of a vaccination program?
- pre-licensing evaluation of a vaccine
2. post-licensing evaluation
What phases does pre-licensing evaluation of a vaccine cover?
- phase I - safety of adult volunteers
- phase II - immunogenicity and reactogenicity in the target population
- phase III - protective efficacy
What does post-licensing evlaution cover?
safety and efficacy of vaccine
disease surveillance
serologic surveillance
measurement of vaccine coverage
What are phase IV trials?
involve post-marketing research to gather more information about risks and benefits of a drug
Can there be more than 3 phases in a clinical trial?
yes - there can be 4
What are the ethical aspects that must happen in human experimentation?
the benefits must outweigh the risks
What are some ethical issues in human experimentation?
informed consent
withholding treatment known to be effective
protect the interest of the individual patient
monitoring for side effects
deciding when to withdraw a patient
What is the CONSORT statement?
this is a protocol that guides the reporting of randomized trials by providing a 22-item checklist and a flowchart
What are some of the strengths of clinical trials?
provide the greatest control over the amount of exposure, the timing and frequency of exposure, and the period of observation
ability to randomize reduces likelihood that groups will differ significantly
What are some of the limitations of clinical trials?
artificial setting
limited scope of potential impact
adherence to protocol is difficult to enforce
ethical dilemmas
What do community trials determine?
the potential benefit of new policies and programs
What is the definition of an intervention program?
any program or other planned effort designed to produce changes in a target population
What does community refer to in community trials?
community refers to a defined unit - like a county, state, or school district
Should a variety of measures be used in community trials?
If so, what are some examples?
yes
examples are disease rates, knowledge, attitudes, and practices
What is the process for community trials?
start by determining eligible communities and their willingness to participate
collect baseline measures of the problem to be addressed in the intervention and control communities
Are community trials randomized and followed over time?
yes
Are outcomes of interest measured in community trials?
yes
What are some of the advantages of community trials?
they represent the only way to estimate directly the impact of change in behavior or modifiable exposure in the incidence of disease
What are some of the disadvantages of community trials?
they are inferior to clinical trials with respect to ability to control entrance into the study, delivery of the intervention, and monitoring of outcomes
fewer study units are capable of being randomized, which affects comparability
they are affected by population dynamics, secular trends, and nonintervention influences
How are quasi-experiment/community trials ranked in strength?
ranked immediately below controlled experiments in rigor
In quasi-experimental/community trials might there be contamination across the conditions of the study?
yes
Under the algorithm for determining study type - what type of study is it when an investigator does assign exposures?
an experimental study
