# Lecture 5 and 7 (Study Types) Flashcards

1
Q

Cohort study definition:

A
• prospective, observational.
• start with no diseases, look at exposure and disease development over time.
• more expensive than case-control.
2
Q

Statistic utilized for cohort study:

A

RELATIVE RISK

3
Q

Cross-sectional study definition:

A
• single time point, observational.
• take a slice of the population
• how many people have a disease or a risk factor right now
4
Q

Statistic for cross-sectional study:

A

POINT PREVALENCE

point prevalence = (total #sick)/(total population)

5
Q

Case-control study definition:

A
• retrospective, observational.
• start with disease and go back retrospectively to find the risk factor
• cheaper than cohort studies
6
Q

Statistic for case-control study:

A

ODDS RATIO

7
Q

Nested case-control study definition:

A
• select cases and controls from a cohort study
• go back and find the risk factor
8
Q

The three types of error in studies:

A
1. random (chance)
2. systematic (bias)
3. confounders
9
Q

Random error:

A
• chance
• will cancel out as sample gets larger
• more likely will lead to type 2 error
10
Q

Systematic error (bias):

A
• cannot be corrected for regardless of sample size
• more likely will lead to a type 1 error
11
Q

Confounder definition:

A
• must be associated with exposure
• must be associated with outcome
• cannot be in the causal pathway between exposure and outcome
12
Q

How can you control for confounding?

A
• At the design stage:
• randomization
• restriction
• matching
• At the analysis stage:
• stratification
13
Q

Selection bias:

A
• nonrandom assignment to groups
• must be controlled at design stage.
14
Q

Healthy worker effect (bias):

A
• workers are generally healthier than the general population.
15
Q

Self-selection bias:

A
• research volunteers different from the general population in terms of their exposure and disease status.
16
Q

Withdrawal bias:

A
• differential loss to follow-up; people drop out
• drop outs may be more sick
17
Q

Recall bias:

A
• knowledge of presence of disease changes subject’s response
18
Q

Sampling bias:

A
• subjects are not representative of population, non-generalizable
19
Q

Confounding bias:

A
• one factor distorts/confuses the effect of another closely related one.
20
Q

Information/observer bias:

A
• researcher’s decision affected by prior knowledge of subject’s exposure.
• Correct for by blinding.
• must be controlled at design stage
21
Q

What forms of bias are case-control studies sensitive to?

A
• recall bias
• selection bias
• observer bias
22
Q

Case-control study benefits:

A
• good for rare diseases
• can test for a wide variety of exposures
• important in understanding new diseases
• commonly used in outbreak investigations
23
Q

Cohort study benefits:

A
• can choose all the variables you want
• can control for bias and confounders
24
Q

How to choose sample for case-control study:

A
• Case definition should not be too broad - misclassifies
• Case definition should not be too narrow - reduces sample size
• Cases and controls should be members of the same base population and have had equal opportunity to have been exposed (same environment).
25
Q

Proces of the development and testing of a new clinical test (index test):

A

need to compare index test to reference test:

1. select patients
2. test all patients with index test
3. test and diagnose all patients with reference test
4. compare index test results with reference test results
26
Q

Potential bias in an index test study:

A
1. utilization of wrong reference test
2. spectrum bias
3. verification bias
4. observer bias
27
Q

Spectrum bias:

A
• applies to index test studies
• patients in study not the same as those found in standard practice
• i.e. using only patients more likely to test positive - will make test look better
28
Q

Verification bias:

A
• applies to index test studies
• not all patients in study receive both the index and reference test
29
Q

Analytical observational studies:

A
• Observe events as they happen in the ‘real world’ without playing an active role in what happens.
• “Incidence” studies
• Two-types:
1. cohort
2. case-control
30
Q

What is a cohort?

A
• a group of people with something in common who are then followed over time to see what happens to them.
• should not have the outcome at enrollment, but should be at risk for it
31
Q

Effect modifiers are:

A
• Effect modifiers are variables that change the effect of the exposure of interest on risk of disease.
• “interaction”
32
Q

Randomization:

A
• an attempt to evenly distribute potential (unknown) confounders in study groups.
33
Q

Restriction:

A
• excludes participants with known confounding variables
• may decrease sample size and power
34
Q

Stratification:

A
• stratify data by a potential confounder, and then compare both groups
35
Q

Matching:

A
• For each subject in the exposed group, one or more patients with the same characteristic (with or without the confounder, eg. smoker or nonsmoker) is chosen for the non-exposed group.
• has to be coupled with a matched analysis
36
Q

Randomized control trial:

A
• prospective, interventional, gold standard
• treatment versus placebo — watch outcome
• statistics: NNT/NNH; multiple comparisons
• four phases
37
Q

Meta-analysis study:

A
• retrospective, chart review, platinum standard
• pools data from multiple studies, usually RCTs
• analyzes cumulative data to determine external validity
38
Q

Twin concordance study:

A

genes versus environment (early life)

• monozygotic = identical twin, same genetic material, same environment
• dyzygotic = non-identical twins, different genetic material, same environment
39
Q

A

genes versus environment (later life)

• come from genetically sick family, raised in completely different environment, but still get sick. Hints to powerful effect of genes.
40
Q

RCT Phase 1:

A

SAFETY

• small # healthy volunteers
• toxicity
• pharmacokinetics
• in cancer, phase I studies will include critically ill/terminally ill patients
41
Q

RCT Phase 2:

A

EFFICACY

• small # patients with disease
• dosing
42
Q

RCT Phase 3:

A

TREATMENT VERSUS CONTROL

• large # patients with disease
• compares standard treatment to novel treatment
43
Q

RCT Phase 4:

A

post-marketing SURVEILLANCE

• after drug has been approved
• watches for rare, long term effects