epidemiology : MC4 - measures of disease frequency

define disease occurence

probability of unaffected individual developing a specified health outcome over a given period of time

(how common a disease is)

define disease frequency

how often a disease or another health event occurs in a population

must 3 factors must be considered when measuring disease frequency and occurrence ?

1. number of people affected

2. size of population

3. length of time

how are ratios expressed ?

1:X (pretty much saying 1/x)

how are proportions expressed ?

fractions expressed as percentages (0% to 100%) / range (0 to 1)

how is rate expressed ?

per unit of time

what are the 2 basic measures of disease frequency ?

incidence & prevalence

what does incidence measure ?

occurence of NEW disease

what does prevalence measure ?

existence of current disease

which measure of disease frequency deals with the transition from health to disease

incidence

which measure of disease frequency focuses on the period of time that a person or population lives with a disease

prevalence

what are the 2 types of incidence measures ?

cumulative incidence & incidence rate

define cumulative incidence

the proportion of a candidate population that becomes diseased over a specific period of time

calculation for cumulative incidence ?

number of new cases of diseases / number of candidate population

what does cumulative incidence NOT take into account ?

dropouts & when individuals developed the outcome

define incidence rate

the occurrence of new cases of disease that arise during person-time of observation

calculation for incidence rate ?

number of new cases of disease / person-time of observation in candidate population

how do you calculate the unit person-time ?

multiplying number of people in study by the time each person spends in the study

what are the 2 different types of prevalence ?

point prevalence

period prevalence