Week 2 - Measuring Disease in Populations Flashcards
What is incidence rate?
No. of new cases of the disease per 1000 people per year (or 1000 person years)
What is prevalence?
Amount of people who currently have the disease in set population (with no time frame)
What is the relationship between incidence and prevalence?
Increase incidence? Cure more patients? Kill more patients? Keep patients alive for longer? P =
Increase prevalence Lower prevalence Lower prevalence Increase prevalence P= I x L
What does incidence measure? What is the limitation?
Measures population’s average risk of disease.
Not all people have same proneness/risk of disease
What are the concepts on the ‘amount’ of disease?
No. of new cases that have occurred - focuses on new events, useful when monitoring epidemics
No. of people affected by the disease - counts people with existing disease (new and old events), describes burden of disease, useful as a measure of need for services
Why do we study systematic variations?
It can give us clues about the aetiology of the disease
How can we find the aetiology of a disease? Why do we look of or the causal factor?
Compare the levels of exposure in two groups of people. Possible to prevent exposure and so reduce incidence of the disease.
How is IRR (incidence rate ratio) calculated?
Compare incidence rates in two groups of different exposure. IRR = (Rate of exposed)/(Rate of unexposed)
What else can IRR be used to calculate and how?
Efficacy of treatment. Exposure is the treatment options (new vs old normally)
Is systematic variation always good? And if so or not, why?
No. Can be used to find cause of disease and efficacy of treatments, but is also a nuisance.
Eg. Of systematic variation being a nuisance.
Age and sex are strong determinants of health. Rate ratio for most diseases comparing (rate old)/(rate young) are usually >1. Old people are more prone to illness
What is a confounder?
Something that is associated with both the outcome and exposure of interest, but is not on the causal pathway between exposure and outcome.
What can confounding explain?
All or part of an apparent association between an exposure and a disease.
How to cut out the nuisance of confounding on age/sex?
Calculate SMR (standardised mortality ratio)
What does SMR compare?
Level of observed mortality in a study pop vs level of expected mortality if standard reference of population’s age-sex specific rates were applied to study population age-sex groups
