research study design. objective- to devise a study method that will clearly answer the study...
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Research Study Design
Research Study Design
Objective- To devise a study method that will clearly answer
the study question with the least amount of time, energy, cost,
and patient risk.
Timing of Observation
Will patients be examined once, or followed over time, allowing for multiple outcome assessments?
Timing of Observations
Only one observation of the risk and outcome variables.
Cross-sectional Study
Timing of Observations
Multiple observations of risk and outcome over time.
Cohort (Longitudinal) Study
Timing of Study Question Development
Will the data be collected from a time period that precedes or
follows the development of the study question?
Timing of Question Development
Question proposed prior to data collection and outcome.
Prospective Study
Timing of Question Development
Question proposed prior to data collection but after the outcome
occurrence.
Retrospective Study
Cross-Sectional Survey
Provides a snapshot view at one instant in time of the relationship
between risk and outcome.
Incidence
A rate at which people develop a given disease or condition over a
specific period of time.
(Ex: Each year, 1000 cases of AIDS occur.)
Prevalence
The proportion of a people who have a given disease at one point in time. It is not a rate, although it is often called a
prevalence rate.
(Ex: Today, 1,000 people have AIDS)
Point Prevalence
The same as prevalence, since prevalence is recorded at one
point at time.
Cross-Sectional Study
• Optimal design when causality not previously suggested.
• Risk/outcome relationship suggested, but not proven by this design.
Case-control Study
The retrospective comparison of patients with different outcomes (diseased, not diseased), with a
retrospective look at risk variables.
Case-control Study
• Matching: Selection process that insures that cases and control subjects are similar with respect to confounding factors.
• Prevents adverse influence on true risk/outcome relationship.
Case-control Study
• Analyze risk variables in both outcome groups.
• Determine if risk is unequally distributed in the cases and controls.
Matching
The process of selecting study and control subjects so that they
are similar with respect to confounding factors.
Confounding Variable
A factor that is related to both the risk variable and outcome that
mediates a change in the apparent association between the exposure and disease (ie:
suggesting an unreal association or masking a real association.
Confounding Variable
A variable more likely to be present in one group of subjects than another that is related to the
outcome of interest and thus potentially confuses, or
“confounds,” the results.
Nested Case-control Study
A case-control study that includes patients who are originally part
of a cohort study.
Risk Variable Manipulation
Will the researchers observe or intervene?
Observational Study
The study of risk variables and outcome without alteration of
any risk variables by the researcher.
Interventional Study
The study of outcome that involves the manipulation of one
or more risk variables by the researchers.
Observational Study
A study that does not involve an intervention or manipulation. It is
called case-control, cross-sectional, or cohort, depending
on the design of the study.
Observational Study
A study which describes risk variables and outcome.
Descriptive
Observational Study
The study of risk variables and outcome which attempts not
only to describe the risk variables and outcome, but also
attempts to determine their relationship.
Analytic
Descriptive Statistics
Statistics such as mean, standard deviation, proportion, and rate used to describe attributes of a
data set.
Randomization
A procedure for assigning treatment to each patient in such
a way that it is equally likely (within the constraints of the
experimental design).
Randomization
Patients are allocated to the treatment and control groups by
chance.
Intervention Plan
Will the interventions be
randomly assigned?
Intervention Delivery
Patients are randomly assigned to different experimental groups
(ie: placebo vs. drug).
Randomized Trial
Intervention Delivery
Patients are not randomly assigned to different experimental groups (ie: placebo vs. drug), but instead are provided different interventions
under the control of the researchers.
Non-randomized Trial
Research Awareness
Do the data collectors know to which experimental groups
patients have been assigned?
Blinding
To deprive of perception or judgment.
Blind Study
An experimental study in which subjects do not know the
treatment patients are receiving; investigators may also be blind
to the treatment patients are receiving.
Single-blinded Trial
Patients do not know to which group they have been assigned.
Double-blinded Trial
Patients and investigators do not know which group each patient
has been assigned.
Double-blinded Trial
A clinical trial in which neither the subjects nor the investigator(s) know which treatment subjects
have received.
Open Trial
A trial in which both the patient and investigator know that they
are receiving the study drug (intervention).
Prophylactic Trials
Trials designed to find ways to prevent the occurrence or
spread of disease.
Therapeutic Trials
Trials designed to find better ways to treat established diseases.