Session 2 - measures of disease occurrence

Question 1

Prevalence

Answer 1

Proportion of people with a disease at given time
Expressed as %

Question 2

Incidence proportion

Answer 2

= cumulative Incidence
New cases / those ‘at risk’ at start of time period
Exclude those who already have it / immune
Requires follow up
Expressed as person/time
eg 0,6/30 years, 0.2/20years

Question 3

Incidence rate

Answer 3

New cases of disease in population per unit person/time among those at risk
Calculate total time at risk - accounts for lost to f/u / death

Question 4

Routine (passive) vs Active surveillance

Answer 4

Passive
Voluntarily reported, ? unknown denomniator

Active
Promted by health agency with a specific response - actively looking for cases or systematic protocol

Question 5

Examples routine and active surveillance

Answer 5

Routine
Notifiable diseases, hospital or GP data

Active
eg case finding COVID-19 - designated teams look for specific condition

Question 6

Point prevalence

Answer 6

Snapshot of condition at a specific point in time
%
People with the attribute/population at risk
Relevant for planning and chronic diseases

Question 7

Period prevalence

Answer 7

% at risk population with condition during a specific time period
Strictly a RATE not a RATIO
= incidence rate x duration event

Question 8

Issues with Cumulative incidence

Answer 8

May have missed events = underestimated numerator
Also assumes all are observed for full follow up - if not true = overestimated denominator
= Underestimates Incidence

Question 9

Epidemiologist’s Bathtub

Answer 9