Life Course Models

Question 1

Define ‘critical period model’.

Answer 1

An exposure in earlier life has lifelong effects on structure or function (which may or may not be modified by later
experience).

Question 2

Define ‘critical period’.

Answer 2

The only time period during which an exposure (A) has an effect, e.g. fetal programming.

Question 3

Define ‘sensitive period’.

Answer 3

A time period during which the exposure has a greater effect than if you’re exposed outside this time period, e.g. learning a second language in childhood, smoking before 1st pregnancy and breast cancer risk.

Question 4

What does it mean by the accumulation of independent risks?

Answer 4

The accumulation of exposure to different, uncorrelated
risk factors (A, B and C) causes long term damage and
increases disease risk.

Question 5

What does it mean by the accumulation of clustered risks?

Answer 5

The accumulation of exposure to different risk factors (A,
B and C) which are clustered (due to association with
another risk factor (D)) causes long term damage and
increases disease risk.

Question 6

Which accumulation of risks is more common, clustered or independent?

Answer 6

Accumulation of clustered risks is more common.

Question 7

What is chains of risk (additive effect)?

Answer 7

Each exposure also has an independent effect on the disease risk whilst increasing each other’s risks.

Question 8

What is chains of risk (trigger effect)?

Answer 8

Earlier exposures influence risk of subsequent exposures but have no effect on the disease risk without the final risk in the chain.

Question 9

List theoretical challenges with these models.

Answer 9

• Careful model building procedure required.
• Traditional models may not be adequate when dealing with factors on the causal pathway.
• Presentation and communication of results.
• Cohort effects.
• Repeat observations – exposures and outcomes.
• Multiple small/interactive effects.

Question 10

Why are life course models useful?

Answer 10

• They help to distinguish between variables acting through different pathways
• They force one to consider the timing (critical), duration (accumulation) and temporal ordering (chains of risk) of exposures