How do we measure disease Flashcards
What are some factors to consider when measuring disease?
- who was attacked ?
- when did the disease occur?
- where did the case arise?
What is incidence?
number of new events in the population over the certain time
What does measuring incidence require?
- requires two or more measurements to individuals were disease free at the start
- measures the number of disease events → measure of risk (accounts for duration of disease)
What is incidence a measure of?
a measure of risk
What is incidence rate?
incidence rate - rate at which susceptible individuals become infected per unit time
What is prevalence?
proportion of individuals in the populations that have the outcome of interest at any given time
What is prevalence a measure of?
measure of burden like taking a slice through the population at any time
What are the challenges with prevalence?
similar challenges as incidence - numerator (who is really infected) denominator (who is actually at risk)
What is point prevalence?
point prevalence-current cases
What is period prevalence?
period prevalence - current cases over a specified period of time
What is the relationship between prevalence and incidence?
Prevalence = incidence * duration of the disease
What is relative risk?
relative risk- the ratio of the risk of disease in exposed individuals to the risk of disease in unexposed individuals - measures the association between exposure and disease
What do the values of RR mean?
- RR =1 - no association
- RR >1 - positive association exposed are more likely to get the disease
- RR <1 - negative association - unexposed are more at risk
What is odds ratio?
odds ration - ration of odds of exposure in diseased vs odds of exposure in non-diseased group
What is transmission?
passing from an infected individual or group to a different individual or group weather the other individual was previously infected
What is a secondary attack?
secondary attack rate - proportion of individual affected individuals infected amongst susceptible hosts in contact with a primary case
Why is there a discrepancy between what we can readily observe and the disease process
There is a discrepancy between what we can readily observe and the disease process. An individual can be infectious before they have clinical symptoms
How do you calculate incidence rate?
of new cases of a disease occurring during a specified period of time/sum of different times that each individual was at risk
how to calculate point prevalence?
(# of cases at a specified point in time/ population at the specified point in time) * 100
What is the formula for relative risk?
incidence in exposed group / incidence in unexposed group
Relative risk calculation from table
see notes
what is the formula for odds ratio?
odds of exposure in exposed group / odds of exposure in disease free group
calculation of odds ratio from table
see notes
what is the formula for secondary attack rate?
of new cases of a disease occurring among primary contact / # total number of contacts
