Disease frequency

Measure of disease frequency

Incidence rate: determines number of new cases of disease

USEFUL FOR HEALTHCARE PLANNING

Need to consider disease relapse and if people are undiagnosed and population instability

Denominator population

people at risk of getting the disease

Comparing rates

Can be misleading to compare rates between calender years if population structure changes can over come with

Standardisation

Comparing by categories e.g age

Stratify: seperate into groups

Prevalence

Focus on disease status depends on disease incidence and duration

Point prevalence: specific point in time

Period prevalence: at mid point of the period

adjust denominator subtracting people that die or leave

between 0-1

risk

Risk can be expressed as probability of outcome / hazard of outcome / incidence of outcome

How can we measure effect

Comparing by absolute measures and relative measure e.g. ratio

Calculating absolute risk

People not eating processed meat already have 5% risk, unexposed

Exposed people risk increases by 20% (1.2) risk ratio

Risk ratio

gives number as a percentage e.g. 4%

Attributable risk

gives the risk in a given population e.g. 150 out of 1000

Number needed to treat

Can indicate ineffective treatment

Number needed to harm

Number of people when treated has harmful outcome. Assesses adverse impacts of a treatment.

•NNH=1/Absolute risk difference

•Always round down to nearest whole number

Survival curves

95% confidence intervals