Measuring Health And Disease Flashcards
Prevalence
Prevalence is the number of cases of a disease in a population at one point in time, as a proportion of the total number of persons in that population.
Number of cases of a disease in a population in a point in time/ total number of persons in that population in that point in time.
Incidence rate X mean duration of disease
Frequency of the population at one moment in time.
That is why it is referred as point prevalence.
It is a proportion and not a rate.
Should always be mentioned in reference to a point in time.
Incidence
Incidence quantifies the number of new cases of disease that develop in a population during a specified period.
Benefits as compared to prevalence: prevalence could vary depending on duration of diseases and new cases. Incidence takes this into account.
A) Cumulative incidence (or Risk)
B) Odds of disease
C) Incidence rates
Cumulative Incidence (risk)
Measures an incidence.
It is the proportion of persons in a population comprised of people who are initially free of disease and who subsequently develop in within a specific time interval.
Number of new cases of diseases in a given time period / number of disease free persons at the start of that time period.
Odds of disease
Number of cases who did become a case of disease in a given time period / number of persons who did not become a case in that period in time.
Measures incidence.
Incidence rates
Problem it solves: in a study participants might join at different times and leave at more times as well.
Number of new case in a given time period / total of persons at risk during that period.
Important to always specify the unit: person-day, person-month etc.
Relative measures of exposure effect
Risk ratio:
Cumulative incidence in the exposed group / cumulative incidence in the unexposed group
Rate ratio:
Incidence rate in the exposed group / incidence rate in the unexposed group
Odds ratio:
Odds of disease in the exposed group / odds of disease in the unexposed group
Risk ration
Relative measure of exposure.
Cumulative incidence in the exposed group / cumulative incidence in the unexposed group
Rate ratio
Relative measure of exposure.
Incidence rate in the exposed group / incidence rate in the unexposed group
Odds ratio
Relative measure of exposure.
Odds of disease in the exposed group / odds of disease in the unexposed group
Absolute measures of exposure effect
Prevalence difference
Prevalence in the exposed - prevalence in the unexposed
Risk difference
Risk in the exposed - risk in the unexposed
Rate difference
Incidence rate in the exposed - incidence rate in the unexposed
Prevalence difference
Prevalence in the exposed - prevalence in the unexposed
Risk difference
Risk in the exposed - risk in the unexposed
Rate difference
Incidence rate in the exposed - incidence rate in the unexposed
Measures of frequency
- Prevalence
- Incidence
- Relation between prevalence, incidence and duration of disease
