Cohort Study Designs

Question 1

Why are cohort studies also known as incidence studies?

Answer 1

Because they detect new cases of disease.

Question 2

Why are cohort studies valuable?

Answer 2

Because they can generate risk ratios and they’re useful for studying rare diseases.

Question 3

What is a cohort study design?

Answer 3

The groups are allocated based on exposure and the outcome or development of disease is what is observed.

Question 4

What are prospective cohorts and what are their downsides?

Answer 4

They allocate their groups based on exposure and wait to see the outcome.

Downsides- more resources- takes longer- more loss to follow up

Question 5

What is a retrospective cohort and what are its advantages?

Answer 5

The researcher starts off knowing who gets the disease but they use old medical records to determine their exposure and allocate groups that way.

Upsides/downsides- takes less time-but you’re at the mercy of the accuracy and availability of the medical records.

Question 6

What is an ambidirectional cohort study?

Answer 6

Uses a retrospective design and after a set amount of time and disease outcome has been determined the researcher decides to continue observing the subjects

Question 7

What is the second way of conducting a cohort study? And give an example.

Answer 7

In a cohort study allocation is based on the fact that a group of people have something in common.

Ex: birth cohort- everybody born in KC in 2014

Question 8

What is an inception cohort and what are examples?

Answer 8

Group allocation based on the people having something in common- ex where they live and where they work.

Ex: nurses, Framingham,MA, during birth delivery sequential instruments were used.

Question 9

What is an exposure cohort? And give an example.

Answer 9

Non-reproduce able event causes a common exposure among people.

Ex: 911 firefighters and 9th ward residents hit by Katrina.

Question 10

What is a fixed cohort study

Answer 10

Fixed cohort-an exposure cohort which means you can’t add new people but you can get loss-to-follow.

Question 11

What’s a closed cohort?

Answer 11

A very short, fixed cohort study with no new people or loss-to-follow.

Ex: A closed room not letting anyone in or out.

Question 12

What’s an open (or dynamic) cohort study?

Answer 12

Some people can be lost and some people can be gained.

Ex: Framingham, new babies and deaths

Question 13

How do you select an exposed study population.

Answer 13

Be sure that you’re following pre-defined criteria of exposure.

Question 14

What must you be sure to do when selecting an unexposed study population?

Answer 14

Make sure that the unexposed group is as close as possible to the exposed group.

Question 15

What are the three sources to finding unexposed groups in cohort studies?

Answer 15

Internal- from the same cohort but unexposed.

General population-unexposed people from the general population.

Comparison cohort- matching groups based on personal characteristics.

Question 16

What are the strengths of cohort studies?

Answer 16

-good for assessing multiple outcomes of one exposure.
-useful when exposures are rare.
-useful in calculating risk and RR
-less expensive than interventional
-good for ethical limits
-good for long incubation periods
-***able to represent temporality (prospective)- gets close to proving causation
-can obtain a greater amount of study-important info from patients.
Follow-up tracking of patients can be easier if you plan ahead.

Question 17

What are disadvantages of prospective cohort studies.

Answer 17

• time, money, and lost-to-follow ups
• not efficient for rare diseases
• not good for long incubation periods
• exposure amount may change over time.

Question 18

What are the advantages of retrospective cohort studies?

Answer 18

• less time money and lost-to-follow ups
• efficient for rare diseases
• good for long induction/latency periods
• useful if the data already exists

Question 19

What are the disadvantages of retrospective cohort studies?

Answer 19

• requires access to charts, databases, and employment records
• Info may not factor in or control for other exposures or harmful events
• Patients may not be available for interview if contact necessary for missing or incomplete data.
• exposure may have changed over time.

Question 20

What are the issues affecting outcome occurrence in groups?

Answer 20

• Level of exposure
• Induction period
• Latency period

Question 21

What are the key biases in cohort studies?

Answer 21

Healthy-worker effect: Only the healthy workers would be at work

Selection bias-misclassification