WEEK 8: DESIGN 3&4 EXPIREMENTAL STUDIES, QUALITIVE STUDIES Flashcards
what are observational studies
researchers collect, record, and analyze the data on participants as they naturally divide themselves by potentially significant exposure and outcome variables.
what are experimental studies
- involve some type of intervention and control of the exposure variable by the researchers to see how this control influences the outcome variable.
- Key feature is that the conditions of the study, particularly the exposure status are directly controlled by the intervention of researchers
6 steps to the process
- Research questions for experimental studies
- Types of experimental studies
- Study population
- Consent, enrollment, exposure assignment
- Minimizing bias
- Analysis
what is a prevention trrial
Agent given to healthy or high-risk individuals to prevent disease occurrence
Ø Does removing lead-contaminated soil prevent lead poisoning in high risk urban children?
what is a therapeutic (clinical) trial
Agent given to diseased individuals to treat or cure disease
Ø Does the drug Herceptin lower the risk of recurrence and improve survival among women diagnosed with breast cancer?
what is an individual trial
Treatment allocated to individuals
Ø Study effectiveness of treatment with two drugs versus three drugs among adults infected with HIV
what is a community (cluster) trial?
treatment allocated to an entire community
how to choose study population
- depends on purpose of the trial
- Specific inclusion/exclusion criteria (eligibility criteria) based on scientific, safety, and practical considerations
o People in population of interest, at risk for outcome, among whom intervention could be effective
o People with a high likelihood of compliance with treatment, likely to be followed for total study period
o May need to exclude certain people, such as those with conditions for which drug under study is contraindicated
what is generalizability
extent to which the results from a study can be generalized (or extended) to people who did not participate in the study
what is the refrence population
group to whom results are applicable/generalizable
- ex. all men and all women
who must approve the study protocol before imitating the procedures
Institutional Review Board (IRB)
what is informed consent?
includes clear explanation of research goals and methods, risks and benefits of participating, assurance of confidentiality, right to withdraw, etc.
what is randomization
each study has the same probability of receiving treatment
How its achieved:
* Toss a coin; heads or tails
* Computer-generated randomization
when are chance differences more likely to occur?
when the study sample is small (<100 per group). In this case, stratified randomization should be considered
what is a cofounder
a factor that distorts the true association between an exposure and outcome
what is blinding/masking
Method of ensuring that participants and/or study investigators have no knowledge of whether a study participant has been assigned to the treatment or comparison group
single, double and triple blind
Single-blind: study participant does not know whether they are receiving treatment or no treatment
Double-blind: neither the (1) study participant nor the (2) study investigator administering the treatment knows who is receiving treatment or no treatment
Triple-blind: neither the (1) study participant nor the (2) study investigator administering the treatment nor the (3) study investigator monitoring the effects of the treatment knows who is receiving treatment or no treatment
why use a placebo?
Ø Makes exposed and unexposed groups’ experiences as comparable as possible (this goal harkens back to lab experiments)
Ø One method of blinding
what is the placebo effect?
Participants assigned to placebo group improve because they are told that they will. This stems from the power of suggestion.
what is compliance
Following the study protocol exactly as required throughout the course of the trial
what are the two goals of compliance
Ø Goal # 1: Have groups be as alike as possible on other important characteristics (randomization)
Ø Goal # 2: Have groups be as different as possible on exposure (intervention)
strengths of randomized control trials
- Demonstrate causal relationships with high level of confidence
o Because of higher validity - Researchers can control exposure levels
weaknesses of randomized control trials
(1) Limited applicability due to ethical reasons and at times due to artificial setting of experiment
(2) Potential for bias due to difference in compliance, withdrawal, and loss to follow-up in experimental and control groups
(3) Usually costly and time consuming
(4) May have limited external validity (low generalizability)
(5) Risk of contamination is high even in blinded studies
community trials
An extension of the cluster and randomized trial where the unit of randomization is a whole community
what is the health research process?
- Research question
- Generate hypothesis
- Identify subjects and variables
- exposure/outcome association - Collect data
- Sample population
- Measure variables
Measurement error and associated misclassification happens here - Analyze data
- Describe data
- Measurement of occurrences/associations - Interpret findings
- Causation
- Bias, confounding - Communicate
- Publish, present
- Report
randomized control trial
some participants are randomly assigned to an active intervention group, remaining participants are assigned to a control group, and all participants from both groups are followed forward in time to determine who has favorable outcomes and who does not
types of success
superiority trial: intervention is better than the comparison
noninferiority trial: intervention is not worse than the comparison
equivalence trial: intervention is equal to comparison
standard of care
an existing therapy used as a comparison for a new therapy being experimentally tested
Hawthorne effect
type of bias that occurs when participants in a study change their behaviour for the better bc they know they are being observed
detection/surveillance bias
occurs when a population group that is routinely screened for adverse health conditions incorrectly appears to have a higher-than-typical rate of disease bc more frequent testing enables higher case detection rate in the population than i the general population
simple randomization
use of a coin toss, a random # generator, simple mechanisms that randomly assign individuals to an exposure group
stratified randomization
the didion of a population into subgroups prior to randomly buy systematically assigning each individual within each subgroup to 1 of the exposure groups
adverse reaction vs adverse event
Adverse reaction - negative side effect of an exposure (i.e medication, vaccination) or a bad outcome related to a study
Adverse event - negative outcome that is the direct result of a study-related exposure or a coincidental occurrence that is not directly related to the study but happens after an individual receives a study-related exposure
efficacy
measure of the success of an intervention that is calculated as the proportion of individuals within the control group who experienced an unfavorable outcome but cold have expected to have a favorable outcome if they were assigned to the active group instead of the control group
what is screening
type of secondary prevention in which all members of a well-define group of people are encouraged to be tested for a disease based on evidence that members of the population are at risk for the disease, and early intervention improves health outcomes
positive and negative predictive value
Positive Predictive Value (PPV) - proportion of people who test positive with the ne test who actually have the disease (according to reference standard)
Negative Predictive Value (NPV) - proportion of people who test negative with the new test who actually do NOT have the disease (according to reference standard)
Which of the following are experimental studies that aim to demonstrate that a new intervention is better than some type of control?
superiority trial
