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Why is it essential to consider a population perspective of healthcare?

All treatments have an impact on others (even if just by cost)
Seeing trends in disease and treatment allows alteration to methods
Knowing needs of a community allows for better planning of services


What is a census?

A record of demographic information collected simultaneously by the government pertaining to all the people living in a particular territory.


Other than census how else might demographic information be gathered?

Smaller surveys - e.g. Household survey, health survey
National registration of births deaths and marriages.


What are the different ways of measuring birth rate?

Crude birth rate
General fertility rate
Total period fertility rate


What is crude birth rate? What use is it?

Number of live births per 1000 population
Used to monitor changes in population size


What is general fertility rate? What use is it?

The number of live births per 1000 women 15-44
Compares fertility of female populations


What is total period fertility rate? What use it?

Average number of children a women would have over her life, calculated by summing fertility rates of each age (year). Hypothetical and assumes rates will stay the same. Compares fertility between groups without interference by age group structure.


Differentiate fertility and fercundity

Fecundity is physical ability to reproduce (influenced by sterilisation, hysterectomy, infertility)
Fertility is the realisation of fecundity (influenced by behaviour, contraception, abortion, economic climate!)


What are the three ways of measuring death rate?

Crude death rate - number of deaths per 1000
Age specific death rate - CDR per age group
Standardised mortality ratio - observed deaths : expected deaths if age/sex distribution of compared populations were identical


What are examples of epidemiological numerator errors?

Changes in diagnostic methods
Changes in disease classification
Changes in protocol (e.g. Death certification)


What are examples of epidemiological denominator errors?

Population used
Boundary changes
Indirect sources (e.g. Counting self reported sick days as illness)


What should be excluded before declaring an observed phenomenon real?

Chance (statistics)
Numerator/denominator error (confounders, bias)
Missing info


Define incidence

Number of new cases per unit time
= new cases / population*time


Define prevalence

Number of people with a disease in a population
= number effected / population


What influences prevalence?

Incidence and length of disease (until cure or death, rapidly fatal diseases have lower prevalences than slow progressing diseases)


What is incidence rate ratio?

Rate in exposed / rate in unexposed

If >1 then exposure may be increasing risk of disease


What does an smr of 106% mean?
What does it not mean!?

An individual has 6% higher risk of death in that population
It does not mean there are 6% more deaths - the population may be younger etc. meaning deaths are actually lower - just that compared to an individual of the same demographics in the other group the risk is higher.


What is the effect of randomness?

The variation of the observed values from the true values. The observed value is our best estimate of the true value


How can observed values be used?

To test a hypothesis about the true value
To provide a probable range in which the true value lies


What is a p value?

The probability that a given result occurred by chance.


What can we infer from a p value of less than 0.05?
How can the two inferences be combined?

Something very unlikely has occured
The nul hypothesis was incorrect

We can say that it is reasonable to reject the nul
We can say that the data is consistent with the stated hypothesis


What can we say if p >0.05?

There is reasonable evidence to reject the stated hypothesis
There is substantive evidence for the nul hypothesis


What are drawbacks of p values?

Small data sets with proportionally the same results as large sets could reach different conclusions
It is an arbitrary value, there is little in actuality different between p=0.049 and p=0.051
Significance does not imply causality or importance


What are the advantages of confidence intervals?

It allows us to determine significance
It gives the range of values we are 95% certain the true value lies within
Reflect the data at level of measurement (i.e. Upper and lower limits given in units applicable to thing being measured)


How do you calculate a confidence interval?

Upper limit - observed x error factor
Lower limit - observed / error factor

Error factor = exp(2xSR(1/observed))


How does the error factor calculation vary between rates, ratios and smr?

Rates - 1/ the lone rate
Ratios - 1/observed a + 1/ observed b
Smr - 1/ observed deaths (ONLY - not expected deaths)


What is the general format of a cohort study?

Recruit disease free exposed and unexposed individuals and monitor for appearance of disease


What are advantages of cohort studies?

Can study rare exposures
Control over what data (demographics, level of exposure confounders etc. collected)
Ability to change data collected if new trends appear
Sequence from exposure to illness


What are disadvantages of cohort studies?

Bad for rare diseases
Risk of loosing participants (loss to follow up and survivor bias)


What are loss to follow up and survivor bias?

Most ill participants may not make it to follow up thus get discounted from results
People making it to the end of a trial may be more likely to have a trait that improves survival - this can act as a confounder - e.g returners for assessment being more health conscious and thus having a healthier lifestyle.