Overview of Study Designs

Question 1

In this type of study, we determine an association between exposure risk and disease of interest, usually NOT causation. **Association is not equal to causation.

Answer 1

Observational Study

Question 2

A lack of random error, which leads to a false association between exposure and outcome just by “chance”.

Answer 2

Precision

Question 3

Lack of bias and confounding.

Answer 3

Validity

Question 4

This is an error committed by the investigator in the design or conduct of a study that leads to a false association between exposure and outcome

Answer 4

Bias

Question 5

A situation in which the relationship between the exposure and outcome is distorted because of the association of exposure with other factor(s) that also influence the outcome under study.

Answer 5

Confounding

Question 6

_____ relates to: The larger the association, the more likely the exposure is causing the disease. For example, the relative risk of lung CA in smokers vs non-smokers is 9 times higher; with further evidence that a relative risk of lung CA in heavy smokers vs non-smokers is even greater at 20 times higher.

Answer 6

Strength of Association

Question 7

The investigator may have inadvertently selected the wrong sample of participants

Answer 7

Selection Bias

Question 8

An error in the assessment process. For example, recall bias of someone who developed food poisoning and cannot remember the food items they ate over the past few days.

Answer 8

Information Bias

Question 9

Name the 3 categories of bias

Answer 9

1. Selection Bias
2. Information Bias
3. Confounding

Question 10

The association is observed repeatedly in different persons, places, times, and circumstances. For example, smoking has been associated w/lung CA in at least 29 retrospective and 7 prospective studies among different population samples.

Answer 10

Consistency

Question 11

_____ is linked to the notion that a single exposure should cause a single disease.

Answer 11

Specificity

causes a SPECIFIC disease

Question 12

_____ means the causal factor must precede the disease in time

Answer 12

Temporality

word is defined as: have a relationship w/time; ex: temporary

Question 13

______ is a DOSE RESPONSE relationship between exposure and disease. Persons who have increasingly higher exposure levels have increasingly higher risks of disease. Ex: lung CA death rates rise w/the number of cigarettes smoked. Some exposures might not have a “dose-response” effect but rather a “threshold effect” below which there are no adverse outcomes.

Answer 13

Biological Gradient

Question 14

_____ and _____ means there is a biological or social model that exists to explain the association. The association does not conflict with current knowledge of the natural history and biology of the disease. For example: we know that cigarettes contain many substances which have been shown to be carcinogenic on their own.

Answer 14

Plausibility and Coherence

Question 15

Investigator-initiated intervention that modifies the exposure through prevention, treatment, or removal should the result show less disease. Example: Smoking cessation programs result in lower lung CA rates.

Answer 15

Experiment

Question 16

This refers to having a similar relationship being observed with another exposure and/or disease. Example: effects of Thalidomide and Rubella on the fetus provide _____ for effects of similar substances on the fetus.

Answer 16

Analogy

Question 17

The 3 most common types of epidemiological study designs are: ____, with ____ having the highest level of causal inference, just below clinical trials

Answer 17

In order from weakest to strongest causal inference:

1. Cross-sectional
2. Case-control
3. Cohort (strongest)

Question 18

**This is an observational study in which exposure and disease are measured AT THE SAME POINT IN TIME in a given population. Cannot establish causation. Highly susceptible to reporting bias.

Answer 18

Cross-sectional study

Hint: The disease and exposure are CROSSING paths/overlapping at the same point in time

Question 19

**This is an observational study in which persons with disease and persons without disease who had the same chance of exposure are studied.

Answer 19

Case-Control Study

Persons with disease (cases) and persons without disease (controls) are studied.

Question 20

**With this type of observational study design, the disease occurs first then the investigator looks back (retrospectively) to determine exposures or risk factors.

Answer 20

Case-control study

Those with the disease (cases) are compared against those who were exposed but did not develop disease (controls)

Question 21

**This is an observational study of persons exposed who develop and persons not exposed who develop the disease. Incidence can be calculated because the exposure comes FIRST and the entire population at risk can be included.

Answer 21

Cohort Study

Question 22

**In this type of study, the exposure occurs first then the determination of disease occurs after the exposure.

Answer 22

Cohort Study

Question 23

For rare diseases, a ____ study may be a poor choice because it may take too long for enough incidences of the disease to occur. Thus, rare diseases might be best studied using a _____ study.

Answer 23

Poor choice: Cohort

Better choice: Case-control

Question 24

In a 2x2 Table, the _____ is across the top (x- axis), and the _____ is along the left (y-axis)

Answer 24

Disease across the top

Exposure along the left

Question 25

These 2 types of study designs utilize a 2x2 table:

Answer 25

1. Case-Control

2. Cohort

Question 26

**With a case-control study, the measure of association is the ____

Answer 26

Odds Ratio (OR)

Question 27

To calculate OR with the 2x2 table:

Answer 27

Multiply across the cells (A x B) and (C x D), then divide those 2 numbers (AxB)/(CxD)

Question 28

With a cohort study, the measure of association is _____

Answer 28

Relative Risk (RR)

Question 29

[A / (A+B)] divided by [C/(C+D)] is the calculation to determine ____

Answer 29

Relative Risk (RR)
the measure of association for a Cohort Study

Question 30

**If a risk in exposed group is greater than the risk in unexposed group, the RR would be:

Answer 30

> 1

Question 31

**If the risk in exposed group is less than the risk in unexposed group, the RR would be:

Answer 31

<1

Question 32

**Odds of exposure in cases (those who have disease) is greater than odds of exposure in controls (those who do not have the disease) would show an OR of ___

Answer 32

OR >1

Question 33

**Odds of exposure in cases (those who have disease) is LESS than odds of exposure in controls (those who do not have the disease) would show an OR of ___

Answer 33

OR <1

Question 34

This measures the likelihood the effect is a result of the exposure or by chance alone.

Answer 34

Confidence Interval

Question 35

What would you look for in a CI to determine if the results are significant?

Answer 35

If the CI includes 1, then it is not significant. Ex: a CI of 0.3 to 3.5 (includes 1 within that range, so it is not significant)

Question 36

For p-Value, we are stating there is only a 5% chance of the outcome occurring by chance alone, so we look for a p-Value of ____

Answer 36

0.05 or less represents significance

Question 37

This test is considered the “gold standard” for a 2x2 table

Answer 37

Fisher Exact Test

Fisher gives you the EXACT results you need
GOLD FISH

Question 38

This is the test of choice when the numbers in the 2x2 table are small (any cell less than 5)

Answer 38

Fisher Exact Test

small fish in a big pond

Question 39

This test can be used when there are at least 30 subjects in the study and at least 5 in each cell of the 2x2 table

Answer 39

Chi-Square Test

There are many people in CHIna

Question 40

How would you write an OR of 1.65 in a sentence?

Answer 40

The odds of having the disease is 65% higher if exposed

Question 41

How would you describe an RR of 3.3 in a sentence?

Answer 41

The risk for disease is 3.3 times higher in those who were exposed.