Lecture 5 and 7 (Study Types)

Question 1

Cohort study definition:

Answer 1

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

Question 2

Statistic utilized for cohort study:

Answer 2

RELATIVE RISK

Question 3

Cross-sectional study definition:

Answer 3

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

Question 4

Statistic for cross-sectional study:

Answer 4

POINT PREVALENCE

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

Question 5

Case-control study definition:

Answer 5

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

Question 6

Statistic for case-control study:

Answer 6

ODDS RATIO

Question 7

Nested case-control study definition:

Answer 7

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

Question 8

The three types of error in studies:

Answer 8

1. random (chance)
2. systematic (bias)
3. confounders

Question 9

Random error:

Answer 9

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

Question 10

Systematic error (bias):

Answer 10

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

Question 11

Confounder definition:

Answer 11

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

Question 12

How can you control for confounding?

Answer 12

• At the design stage:
  
  • randomization
  • restriction
  • matching
• At the analysis stage:
  
  • stratification
  • multivariable adjustment (regression)

Question 13

Selection bias:

Answer 13

• nonrandom assignment to groups
• loss to follow up
• must be controlled at design stage.

Question 14

Healthy worker effect (bias):

Answer 14

• workers are generally healthier than the general population.

Question 15

Self-selection bias:

Answer 15

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

Question 16

Withdrawal bias:

Answer 16

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

Question 17

Recall bias:

Answer 17

• knowledge of presence of disease changes subject’s response

Question 18

Sampling bias:

Answer 18

• subjects are not representative of population, non-generalizable

Question 19

Confounding bias:

Answer 19

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

Question 20

Information/observer bias:

Answer 20

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

Question 21

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

Answer 21

• recall bias
• selection bias
• observer bias

Question 22

Case-control study benefits:

Answer 22

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

Question 23

Cohort study benefits:

Answer 23

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

Question 24

How to choose sample for case-control study:

Answer 24

• 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).

Question 25

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

Answer 25

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

Question 26

Potential bias in an index test study:

Answer 26

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

Question 27

Spectrum bias:

Answer 27

* 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

Question 28

Verification bias:

Answer 28

* applies to index test studies * not all patients in study receive both the index and reference test

Question 29

Analytical observational studies:

Answer 29

* 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

Question 30

What is a cohort?

Answer 30

* 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

Question 31

Effect modifiers are:

Answer 31

* Effect modifiers are variables that change the effect of the exposure of interest on risk of disease. * "interaction"

Question 32

Randomization:

Answer 32

* an attempt to evenly distribute potential (unknown) confounders in study groups.

Question 33

Restriction:

Answer 33

* excludes participants with known confounding variables * may decrease sample size and power

Question 34

Stratification:

Answer 34

* stratify data by a potential confounder, and then compare both groups

Question 35

Matching:

Answer 35

* 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

Question 36

Randomized control trial:

Answer 36

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

Question 37

Meta-analysis study:

Answer 37

* retrospective, chart review, platinum standard * pools data from multiple studies, usually RCTs * analyzes cumulative data to determine external validity

Question 38

Twin concordance study:

Answer 38

**genes versus environment (early life)** * monozygotic = identical twin, same genetic material, same environment * dyzygotic = non-identical twins, different genetic material, same environment

Question 39

Adoption study:

Answer 39

**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.

Question 40

RCT Phase 1:

Answer 40

**_SAFETY_** * small # healthy volunteers * toxicity * pharmacokinetics * in cancer, phase I studies will include critically ill/terminally ill patients

Question 41

RCT Phase 2:

Answer 41

**_EFFICACY_** * small # patients with disease * dosing * adverse reactions

Question 42

RCT Phase 3:

Answer 42

**_TREATMENT VERSUS CONTROL_** * large # patients with disease * compares standard treatment to novel treatment

Question 43

RCT Phase 4:

Answer 43

**_post-marketing SURVEILLANCE_** * after drug has been approved * watches for rare, long term effects