Lecture 4 Flashcards
Describe a disease event/occurrence
A dis-ease event occurs when a person changes from having no dis-ease to having dis-ease.
Typically start of with no disease within denominator, then some get dis-ease (this transition is called dis-ease occurrence)
Sometimes it is possible to observe the change from no dis-ease to dis-ease and sometimes it is only possible (or easier or more useful) to measure if a dis-ease event has occurred after the event
What are the two epidemiological measures of dis-ease frequency to cover the two situations (whether it is easy to observe event)
Incidence and Prevalence
Describe incidence
‘Incidence’ counts observable dis-ease events as they occur over a period of time - basically just think rates (e.g. deaths per year in Swedish soldiers)
Death occurrence is always incidence - as difficult and not useful to measure deaths at one point in time
Describe prevalence
‘Prevalence’ measures how many people have a dis-ease at a point in time (e.g. proportion of New Zealanders with diabetes now).
When measuring prevalence, generally ask about past - have they experience the same event before
When you can’t observe an event occuring easily, measure prevalence. Most diseases are on a continuum - hard to tell when the dis-ease occurrence happens)
Describe categorical
Split into definite categories
E.g. yes or no
Describe numerical
A measure in numbers
Numerical numbers could be turned into categorical measures (e.g. high or low)
What type/s of measures are incidence measures
Categorical
What type/s measures are prevalence measures
Prevalence measures can be both numerical or categorical measures
You can:
- Measure prevalence by finding how many people are in one (e.g. high blood pressure) category and divide by population no.
- Measure prevalence by finding the average heart rate of a population (sum of heart rate/pop no.)
What types of measures can you take in a cohort study
In a cohort (prevalence) study you can measure both incidence measures and prevalence measures (as you can take a prevalence measure at the very start and take an incidence measure over the period of time)
What measures can you take in a cross sectional study
In a cross sectional study you can only measure prevalence measures (as you cannot come back)
What are the strengths and weaknesses of prevalence measures
Strength of prevalence is that it is easier/cheaper
Weakness is that people can be cured or die of a condition and not count within the numerator
What are the strengths and weaknesses of incidence measures
Strength of incidence is that people cannot ‘leave’ the numerator - even if they die or are cured.
Weakness is the expense
