Disease Detective L4 + 12: Measures of Association + Morbidity + Case Control/Cohort

ratio

comparison of two separte numbers where the numerator is not necessarily part/related to denominator

proportion (attack rate is an example)

a ratio where the numerator is included inside the total denominator, expressed as fraction or percentage

rate

measure of the frequency of an event in a population over time, speed of disease + how fast new cases are occuring,

how do we express rate in epidemiology

person-year, how fast new cases are occuring

morbidity

refers to state of illness, diability, disease in a POPULATION

incidence

measures new cases of disease in an appearing population over a period of time, reflects the risk of contracting disease

prevalence

measures the total number of current cases (new + preexisting) in a population in a specific point or period of time, reflects disease burden

morbidity formula: incidence proportion → the risk that an individual will develop the disease over a given timeframe
(numerator=, denominator=)

numerator = number of new cases during a specified time interval

denominator = population at risk at the start of the interval

morbidity formula: secondary attack rate → measure disease within a closed group (house)
(num=, den=)

num: # of new cases among contacts
den: total # of contacts

morbidity formula: incidence rate → measures how fast new cases occur accounting for the differing follow-up times
(num=, den=)

num = # of new cases during time interval
den = # summed person-years of observation (time when they were health + at risk)

morbidity formula: point prevalence → a snapshot of disease burden at one specific date/time
(num=, den=)

num= # of current cases (new + existing) at single point in time
den = population at that exact point in time

morbidity formula: period prevalence → disease burden across an extended window (years, decades)
(num=, den=)

num = number of current cases (new + existing) over specified time period
den = total or average mid-interval population

mortality measures types

crude death rate, cause-specific death rate, proportionate mortality, death-case ratio, infant mortality rate

natality measure types

crude birth rate, crude fertility rate

What type of analytic studies do epidemiologist use to evalute hypotheses?

cohort studies, case control studies

when are cohort studies used + direction

small well-defined population, exposure status to who develops illness (cases)

attack rate

percentage of a specific group that gets sick during a short outbreak

cohort study table variables

a = exposed, sick, b = exposed, not sick
c = unexposed, sick d= unexposed, not sick

exposed attack rate (ppl sick)

a/a+b

unexposed attack rate

c/c+d

relative risk

Compares the risk of getting sick in an exposed group versus an unexposed group

cohort relative risk formula

attack rate exposed/ attack rate unexposed

Cohort: Interpreting Relative Risk (RR>1.0, RR =1.0, RR<1.0)

RR>1.0 → exposure increases risk of illness

RR =1.0 → risk is identicle in both groups

RR<1.0 → exposure is protective and can prevent illness

case control when to use + direction it analyzes from

widespread outbreak where overall population in not well defined, illness status to determind past exposure

odds ratio

Compares the odds of an event happening in one group versus another

Odd Ratio for Case Control studies: worded formula

odds of exposure in cases/odds of exposure in controls

Case-Control: Interpreting Relative Risk (RR>1.0)

RR>1.0 → indicated higher odds of exposure among sick cases than healthy controls