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What is a census?

A simultaneous recording of demographic data by the govt at a particular time, pertaining to all the people living in a particular territory.


What are the main features of a census?

Run by government
Universal coverage
Occurs at regular intervals


What are censuses used for?

1). Allow allocation of resources
2). So we can make projections on populations
3). Work out trends in populations


What is crude birth rate?

The number of live births per 1000 of the population.


What does crude birth rate give us?

It gives us the impact of births on the population size.


What is general fertility rate?

The number of live births per 1000 females of ages 15-44.


What does GFR compare and how is it affected?

It compares fertility of fertile female populations and is affected by age distribution.


What is total [period] fertility rate?

The average number of children that would be born to a hypothetical woman in her lifetime.


What does TPFR compare and how?

It compares the fertile females fertility without being influenced by age structure, by giving each age group equal weighting in its calculation.


What is the calculation for TPFR?

TPFR = sum of (all age specific fertility rates)

e.g. If 24 15yr olds have 6 babies = 6/24 = 0.25


What is fecundity and what affects it?

The ability of a population to reproduce.
Affected by sterilisations and hysterectomies.


What is fertility and what affects it?

It is the recognition of fecundity as a potential for live births.
Affected by sexual activity, the economic climate, abortion and availability of contraception.


What is crude death rate?

The number of deaths per 1000 of the population.


What is age specific death rate?

The number of deaths per 1000 in a particular age group.


What is the standardised mortality rate calculation?

Number of observed deaths in study pop
--------------------------------------------- x 100
Number of expected deaths in study pop


What is standardised mortality ratio and what is its purpose?

A comparison of the observed deaths with the number of deaths expected if 2 populations had the same age-sex distribution.
It adjusts for age-sex confounding by comparing a population with a standard reference.


How do you calculate person years?

It is the sum of total years exposed per person. e.g. 1 person for 10 years, 3 people for 0.1 years
= (1x10) + (3x0.1)


What is a population estimate?

Applying birth rates, death rates and migration to the present.


What is a population projection?

Applying birth rates, death rates and migration to make predictions about the future along with additional assumptions.


What is incidence and its units?

Units are rate
Incidence is the amount of new cases of a disease in a population in a time.


How do you calculate incidence rate?

new events
IR = ------------------------------------
persons x time (years)


What are incidence measurements useful for?

Monitoring epidemics.
Giving a measure of the populations average risk of disease (although people vary)


What is prevalence and its units?

The number of existing cases in a population

~ (incidence x length of disease)

Unit is a proportion (no. cases/population) = no time element.


When can variation aid a study?

1). Systematic variation can give us clues about the cause of a disease e.g. Exposure levels between 2 groups can be used in studies.

2). IRR allows us to compare groups.


How do you calculate IRR and what is it useful for?

Rate of exposed
IRR = -----------------------
Rate of unexposed

It allows us to compare incidence of disease between 2 groups or to compare the efficacy of two treatments.


Why does IRR only give us relative risk?

The value it gives us is comparison between 2 groups only (risk of developing the disease n exposed group compared to the risk in the 2nd group, which I selected). This means it isn't taking into account the general population, and the 2 groups may be systematically different from these.


Why does IR provide absolute risk?

Because it compares the number of new events to the general population


When is variation a nuisance?

Confounding can explain all/part of an apparent association.


How do you eliminate age-sex confounding?

Age-sex confounding always needs to be eliminated.
Use the SMR (compares number of observed deaths to a reference population like the one being studied)
Could use age specific rates but this would be very time consuming as you would obtain many different values.


When is a p value statistically significant?

When p<0.05