Epidemiology and critical skills Flashcards
How do you work out the rate of a condition?
The denominator is the population size. - you must use that (cases per thousand) and not the absolute number
What is descriptive epidemiology?
WHO got WHAT, WHERE? aka time, person, place studies. Surveys to identify who your patients are, where they are getting ill and what is making them ill.
What is the incidence RATE?
number of new cases in specified period DIVIDED BY
sum of length of time during which each
person in the population is at risk
Explain how to calculate the denominator when calculating incidence rate
denominator takes into account not just the number of negative patients at the start, but how long each patient remains negative, until they:
become positive
leave the programme (moves away or dies)
gets to the end of the period of observation still negative
Where do you calculate the point of infection when calcucating incidence rate?
midway between last negative and first positive test result
What is incidence RISK?
incidence risk: number of new cases in specified period DIVIDED BY
population disease-free at start of period
of observation
Problems with incidence risk?
Incidence risk is easier to calculate than incidence rate
simply count how many people you start with
and count how many have developed your outcome disease at the end
This works fine if all the people you start with can be found and checked to
see if they have your outcome disease of interest
If they can’t be found – they are lost to follow-up – then you can’t verify them
as diseased or disease-free – so your numerator lacks accuracy
Benefits of incidence risk versus rate?
Risk is easier to calculate but less accurate. Rate is a ballache to calculate but if someone is lost to followup their months of data can still be taken accurately to show what we knew, and gives you a “risk per month” understanding of incidence rather than absolute.
Definition: Prevalence
the number of cases of a disease in a defined population at a given point in time
Definition: Incidence
the number of new cases of disease arising in a defined population during a specified period
of time
What are the three types of data which determine what statistical tests are required?
Categorical, continuous and continuous skewed
When use “mean” and when use “median”?
Mean will be distorted in skewed data, median won’t. Therefore always use median when dealing with skewed data.
Risk Ratio definition
Risk in group 1/Risk in group 2
so if 20 0f 100 people have a disease in group one, and 60 of 100 in group 2, its (20/100) / (60/100) = risk ratio of 0.3
Odds ratio definition
Odds in group 1/Odds in group 2.
so if 20 0f 100 people have a disease in group one, and 60 of 100 in group 2, its (20/80) / (60/40) = 1/1.5 = 0.33
