Measures of Occurrence Flashcards

1
Q

What is meant by epidemiology?

A

The study of how often diseases occur in different groups of people and why

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2
Q

What is a key feature of epidemiology?

A

the measurement of disease outcomes in relation to a population at risk

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3
Q

What types of definitions are needed?

A

Clear definitions

e.g. “cancer” is not specific enough, need to consider sub-types

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4
Q

What must be defined?

A

the unit of measurement

e.g. a whole country, one hospital

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5
Q

What is meant by checking whether individuals are “eligible” for inclusion?

A

If someone moved from outside the study area with a pre-existing condition, they can be counted for prevalence but NOT incidence

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6
Q

How is disease occurrence usually expressed?

A

as a percentage

or a rate (e.g. number per 100,000 population)

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7
Q

What is the definition of an incidence of a disease?

A

the rate at which new cases occur in a population during a specified period

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8
Q

What is the calculation for incidence rate?

A

number of new cases in a period

/

number at risk in population in the period

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9
Q

What is essential to incidence?

A

It MUST include a time unit

e.g. 1 month, 5 years etc.

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10
Q

What is meant by prevalence?

A

the proportion of existing cases

this includes newly diagnosed cases and people who already have the condition

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11
Q

Why is prevalence useful for public health professionals?

A

It describes the burden of disease

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12
Q

What is meant by point prevalence?

A

The proportion of existing cases in a population at a single point of time

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13
Q

What is meant by period prevalence?

A

The number of new and existing cases over a set period e.g. one year

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14
Q

What is the only way that prevalence can be measured?

A

Cross-sectional surveys

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15
Q

How can prevalence be derived approximately?

A

by calculating:

incidence rate x average duration of disease

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16
Q

What is the difference between population and incident cases?

A

Population is the denominator population

Incident cases are new cases of the disease

17
Q

What factor must be accounted for in the population?

A

In-migration

This is someone who has moved to the area but has not yet been diagnosed

18
Q

What types of people will be in the prevalence pool?

A

The cases living in the population with the disease

This is incident cases, in-migration and the existing population

19
Q

What needs to be excluded from the prevalence pool?

A
  1. out-migration
  2. deaths
  3. cures
20
Q

Why is the denominator population constantly changing?

A

People are constantly moving in and out of the area

21
Q

What is meant by mortality?

A

the incidence of death from a disease

the number of people dying from a disease in a given time period

22
Q

What is the calculation for mortality rate?

A

number of people who die from the disease in a time period

/

number of people in the population in a time period

23
Q

Where are details about individual deaths recorded?

A

on a death certificate

24
Q

What is meant by ascertainment?

A

this means that you have counted all the individuals in your study

25
What can negatively affect ascertainment?
missing medical records poor record keeping changes in how diseases are classified might mean individuals might not be counted or the wrong ones might be included
26
What are examples of common of denominators?
1. population of a country/region 2. number of live births/stillbirths 3. number of patients attending a hospital 4. GP practice population
27
What would be an example of a denominator involving mortality rate in children?
mortality rate per 1000 live births
28
What is meant by crude rate?
a rate that refers to the population as a whole
29
What method is used to compare areas with different population structures?
standardisation this is mainly by age and sex
30
What are the 2 methods of standardisation?
direct indirect
31
What is involved in direct standardisation?
applying the rates of disease observed in the study group to a standard population
32
What is a standard population?
WHO standard populations contain data about people in different countries/world/etc.
33
What is involved in indirect standardisation?
applying the rates of disease in a 'standard' population to the study group
34
How is indirect standardisation usually presented?
it compares observed values to expected values as a ratio e.g. standardised mortality ratio (SMR)
35
What is the calculation for SMR?
observed number of deaths / expected number of deaths