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WEEK 3:
Measuring disease in populations:
| Question | Answer |
|---|---|
| prevalence | number of existing cases in a defined population at a specific point in time |
| incidence | number of new cases arising in a given period in a specified population |
| risk = | cumulative incidence = (number of new cases of disease in time period) / (number of people initially disease free) |
| incidence rate = | number of new cases of disease/ total person time at risk |
| what is total person time at risk | the sum of all the weeks/years etc that people in the study were at risk recorded |
| if you increase incidence? | prevalence increases |
| if you cure more patients? | prevalence lowered |
| if you kill more patients? | lower prevalence |
| if you keep them alive longer? | increased prevalence |
| numerator can be affected by (3) | diagnostic accuracy (some cases may be missed or overdiagnose), changes in case definition, and changes in recording systems (methods of recording cases change over time) |
| denominator can be affected by (3) | population movement (population changes in number or some groups go uncounted), changes in population structure within areas (age/sex structure may change), and changes in administrative boundaries (geographical boundaries like countries change) |
| ecological study | looks for associations between variables at population level (eg USA vs UK) with data often being taken from existing published statistics eg censun data or birth certificates |
| r= | pearson correlation coefficient (degree of linear relationship) (-1 to +1) |
| -1 pearson value | perfect negative linear relationship |
| +1 pearson value | perfect positive linear relationship |
| r^2 | % of variation in the dependent variable that is explained by the independent variable |
| r=0 | null hypothesis (no correlation) |
| advantages of ecological studies (3) | Cheap, quick to perform, Uses existing data and Usually no ethical approval needed |
| limitations of ecological studies (4) | if significantly correlated on population level this could be because: exposure causes outcome, outcome causes exposure, one of more confounders are responsible or ecological fallacy |
| ecological fallacy | incorrect assumption that an association seen at population level holds at an individual level |
Created by:
22tango
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