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Y2 RESS > Measures of Occurrence > Flashcards

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
Q

What can negatively affect ascertainment?

A

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
Q

What are examples of common of denominators?

A
  1. population of a country/region
  2. number of live births/stillbirths
  3. number of patients attending a hospital
  4. GP practice population
27
Q

What would be an example of a denominator involving mortality rate in children?

A

mortality rate per 1000 live births

28
Q

What is meant by crude rate?

A

a rate that refers to the population as a whole

29
Q

What method is used to compare areas with different population structures?

A

standardisation

this is mainly by age and sex

30
Q

What are the 2 methods of standardisation?

A

direct

indirect

31
Q

What is involved in direct standardisation?

A

applying the rates of disease observed in the study group to a standard population

32
Q

What is a standard population?

A

WHO standard populations contain data about people in different countries/world/etc.

33
Q

What is involved in indirect standardisation?

A

applying the rates of disease in a ‘standard’ population to the study group

34
Q

How is indirect standardisation usually presented?

A

it compares observed values to expected values as a ratio e.g. standardised mortality ratio (SMR)

35
Q

What is the calculation for SMR?

A

observed number of deaths

/

expected number of deaths

Y2 RESS (9 decks)

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