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Systematic Reviews

Report on several studies all combined into one (summarized)



Analyzing the data from multiple studies



Bench or animal research; prior to human investigation


Phase 0

Assess drug target actions and possibly pharmacokinetics in single or few doses, healthy or diseased patients, very small population size (less than 20), very short duration (a few days)


Phase 1

Assess safety/tolerance and pharmacokinetics of one or more dosages, healthy or diseased volunteers, small population size (20-80), short duration (just a few weeks)


Phase 2

Assess effectiveness and safety/tolerability, diseased volunteers, larger population size (100-300), short to medium duration (a few weeks to a few months)


Phase 3

Last phase before FDA approval; assess effectiveness and safety/tolerability, diseased volunteers and can include comparison groups for delineation of effects, larger population size (500-3000), longer duration (a few months to a year or more)


Phase 4

Post FDA approval; assess long term safety, effectiveness, optimal use (risks/benefits), diseased volunteers, very large population size (a few hundred to a few hundred thousand), wide range of durations (a few weeks to several years)


Pros and Cons of Interventional Studies

Pros: Cause precedes effect (can demonstrate causation), only designs used by FDA for approval process

Cons: Cost, complexity/time, ethical considerations, generalizability/external validity (is study population similar to general population and will methodology and findings be applicable to them)


Exploratory Study

1 treatment per group; no changing groups, treatments, drugs


Explanatory (Pragmatic) Study

More flexible in their design; can change treatments or drugs between groups; more clinical type approach


Simple Study Design

Divides (randomizes) subjects exclusively into 2 or more groups; single randomization process; no subsequent randomized divisions; commonly used to test a single hypothesis at a time


Factorial Study Design

Divides (randomizes) subjects into 2 or more groups and then further sub-divides (randomizes) each of the groups into 2 or more additional sub-groups; used to test multiple hypotheses at the same time


Parallel Study Design

Groups simultaneously and exclusively managed; no switching of intervention groups after initial randomization; all simple and factorial study designs are also parallel


Cross-Over (Self-Control) Study Design

Groups serve as their own control by crossing over from one intervention to another during the study


What combinations can interventional studies be?

Simple, Parallel
Simple, Cross-Over
Factorial, Parallel
Factorial, Cross-Over



Time between leaving first treatment group in a study and entering second group in the study`



All study subjects blindly given one or more placebos for initial therapy (defined time-period) to determine a "new" base-line of disease (standardization); can assess study protocol compliance, wash out existing medications, and determine amount of placebo effect


Disadvantages of Cross-Over Design

Only suitable for long-term conditions which are not curable or which treatment provides short-term relief

Duration of study for each subject is longer

Carry-over effects during cross-over (wash-out required which prolongs study duration)

Complexity in data analysis


Primary Outcomes

Most important, key outcomes; main research question used for developing/conducting study


Secondary/Tertiary/etc. Outcomes

Lesser importance yet still valuable; possible for future hypothesis generation


Composite Endpoint

Combines multiple endpoints into a single outcome; could be considered the primary outcome, and if so, then secondary outcomes may be the individual outcome elements from composite


Patient Oriented Endpoints

Most clinically relevant; death, stroke, heart attack, hospitalization, preventing need for dialysis


Disease Oriented Endpoints

Elements used in place of evaluating patient-oriented endpoints; blood pressure (for risk of stroke), cholesterol (for risk of heart attack), change in SCr (for worsening renal function)


Non-Random Group Allocation

Subjects don't have an equal probability of being selected or assigned to each intervention group


Random Group Allocation

Most common; subjects do have an equal probability of being assigned to each intervention group


Purpose of Randomization

Make groups as equal as possible; based on known and unknown important factors (confounders); equality of groups is NOT guaranteed


Simple Randomization

Equal probability for allocation within one of the study groups


Blocked Randomization

Ensures balance within each intervention group; used when researchers want to assure that all groups are equal in size


Stratified Randomization

Ensures balance with known confounding variables such as gender, age, disease severity/duration