Cohort Studies

Question 1

Cohort study definition

Answer 1

Cohort studies define and measure the risk factor and then evaluate the outcome in a suitable demographic group over time (you get to pick the people), outcome can be the presence or absence of disease associated with a single RF (not multiple)

Question 2

What is a major difference between Cohort and CCS?

Answer 2

Cohort studies have a well defined population in demographics and numbers. Bias and confounding controlled better

Question 3

What are the two types of cohort studies?

Answer 3

prospective and retrospective

Question 4

What is usually done before a cohort study?

Answer 4

a case control study

Question 5

What is ideal for the control group?

Answer 5

It is ideal for the control group to have no exposure to the RF. Best if personal interviews are performed. Can be complicated if using published data or environmental RF.

Question 6

What is the key point for Cohort studies?

Answer 6

Presence or absence of risk factor is determined before outcome occurs

Question 7

How do you calculate risk?

Answer 7

a/(a+b)

Question 8

How do you calculate relative risk?

Answer 8

a/(a+b) / c(c+d) =

Question 9

How do you form a 2x2?

Answer 9

Risk factor on side and Disease on top

Question 10

What does a RR of 6 tell you?

Answer 10

6x more likely to get disease if exposed

Question 11

Odds Ratio calculation

Answer 11

(a/c) / (b/d), include an error factor

Question 12

Person Years

Answer 12

This adjusts for the amount of time that any individual member of the cohort’s data is available; some in study longer, evaluate number of person years instead of number of people

Question 13

Confounding in Cohort studies

Answer 13

Associations between risk factors and cardiovascular disease outcomes are confounded by pre-existing cardiac, renal and other diseases

Question 14

Bias

Answer 14

Anything that might negatively affect the representativity of the cohorts studied

Question 15

Information bias

Answer 15

Is information about outcome obtained in the same way for those exposed and those not?

Question 16

Features to look for in cohort studies

Answer 16

1. What steps were taken to minimize information bias?
2. How complete was the follow up in both groups?
3. Were potential confounding factors sought and controlled for in the analysis?

Question 17

Cohort vs Case study

Answer 17

Long term and require a lot of planning, less useful in study of diseases of low prevalence or exposure, deals better with confounding and bias, strength of association of RR stronger than OR

Question 18

Why can you extrapolate the results in a case control study?

Answer 18

the demographic latitudes inherent in control group formation and the additional variation built into the confidence interval by including factorials for control groups

Question 19

Clinical trials

Answer 19

A cohort study in which the exposure to the effector is controlled. (Placebo controlled, single/double/triple blind)

Question 20

Triple blind experiment

Answer 20

Patient, clinician, and lab analyzing does not know groups

Question 21

Diagnosis can be made through?

Answer 21

quantitative or qualitative, subjective or objective methods: serology assays, PCR, X-Ray, CAT scans, experience

Question 22

2x2 Table for test sensitivity and specificity

Answer 22

side has test positive and negative; top has disease positive and negative

Question 23

How to calculate sensitivity from 2x2?

Answer 23

a / total disease positives

Question 24

How to calculate specificity from 2x2?

Answer 24

d / total disease negatives

Question 25

Sensitivity tests…

Answer 25

true postives

Question 26

Specificity tests….

Answer 26

true negatives

Question 27

How is true disease status determined?

Answer 27

By a gold standard method

Question 28

How do specificity and sensitivity relate?

Answer 28

Inverse; as sensitivity increases specificity decreases

Question 29

Sensitivity definition

Answer 29

the capacity of the test to correctly identify diseased individuals in a population; true positives. Greater sensitivity means smaller number of false negatives.

Question 30

Specificity definition

Answer 30

the capacity of the test to correctly exclude individuals who are free of the disease, true negatives; the greater specificity means the fewer false positives

Question 31

Positive predictive value

Answer 31

the probability of the disease being present, among those with positive diagnostic test results

Question 32

Negative predictive value

Answer 32

the probability that the disease was absent among those whose diagnostic test results were negative

Question 33

positivity rate =

Answer 33

total positives/total tested x 100

Question 34

negativity rate =

Answer 34

total negatives/total tested x 100

Question 35

Reliable and reproducible results?

Answer 35

How often using the same tests and samples will you get the same results; different test lots, different personnel, equipment variation

Question 36

Misclassification

Answer 36

the placement of subjects into inappropriate group or classification; occurs when the means by which we measure risk are not perfect; may reduce the true value of OR or RR, highlights the need to know the limits and parameters of assessment

Question 37

Non-random misclassification

Answer 37

when exposure or disease status influences group assignment; typically insert unwarranted bias