HADPOP L3.1 MEASURING DISEASE IN POPULATIONS Flashcards

1
Q

What are the two different interpreations of the question “how much disease is there,” and why are they useful to know?

A

a) the number of new cases that occurred
- focuses on NEW EVENTS
- useful when monitoring pandemics

b) The number of people affected by the disease
- counts PEOPLE with EXISTING DISEASE
- describes burden of disease
- useful as a measure of need for services

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2
Q

Define incidence, providing the associated equation

A

Incidence
Measuring rate of new cases
Ex. 300 heart attacks in 50,000 dye workers over 1.5 years
Incidence rate = new events/person x time (years) = events per persons per year

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3
Q

Define prevalence and why is not considered a rate?

A

Prevalence
Measuring existing cases
Prevalence is a proportion NOT a rate
Denominator is PERSONS not PERSONS per time

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4
Q

What is the realtionship between prevalence and incidence?

A

Prevalence = Incidence x Length of Disease

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5
Q

What is systematic variation in rates of disease?

A

The differing levels of non-random risk which exist between different groups of people

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6
Q

How is Systematic variation helpful in understanding aeitology of disease?

A

Compare levels of exposure in two groups of people and identify causal factor for a disease. Having identified causal factor, possible to prevent exposure and thus decrease incidence

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7
Q

How can you compare incidence rates between different groups, and why is it useful

A

Compare incidence rates via Incidence Rate Ratio (IRR)
RateB(exposed)/RateA(unexposed)
If incidence rate in group B higher than rate in group A, implies difference exposure was associated with the difference in rates of disease

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8
Q

How can systematic variation be used to determine efficacy of treatment?

A

Incident Rate Ratio used
Exposure is treatment A (old treatment) or B (new treatment)
Mortality rate ratio = RateB/RateA

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9
Q

What is rate a measure of?

A

Absolute risk

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10
Q

What is ratio a measure of?

A

Relative risk

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11
Q

Why could systematic variation be considered a nuisance?

A

Confounding factors such as age and sex, which are non modifiable and strong determinants of health, are variants but not particularly useful as cannot be changed.

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12
Q

Why is a confounding factor a nuisance?

A

Confounding factors can explain ALL or Part of an apparent association between an exposure and a disease

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13
Q

How would you deal with confounding by age?

A

Could use age specific rate raitos – For instance, use age bands (20-24, 25-29)
Narrow age bands, little confounding due to age occurs, so rate ratios more like to be valid

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14
Q

What would be the issue when using age bands?

A

results are difficult in interpret as too many answers (one from each age band)

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15
Q

What is Standardised Mortality Rate?

A

Indirect SMR is a summary figure comparing OBSERVED levels of mortality with EXPECTED levels of mortality if a standard reference populations age-sex specific rates were applied to the study populations age-sex groups

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16
Q

Why is SMR useful?

A

Accounts for age-sex confounding

17
Q

How is SMR usually expressed?

A

as a percentage

  • 100 = same risk in study population as in reference populations
  • > 100 = higher risk in the study population (SMRs can be expressed relative to 1)