Frequency measures Flashcards
Each row is called a ____
contains information about one individual
“record” or “observation.”
Each column is called a ____
contains information about one characteristic such as race or date of birth
“variable.”
In epidemiology, many nominal variables have only two possible categories:
alive or dead
case or control
exposed or unexposed …… Such variables are called ___
dichotomous variables
The frequency measures we use with dichotomous variables are ___
ratios, proportions, and rates = (x/y) x 10^n
In a ___ , the values of x and y may be completely independent, or x may be included in y.
ratio
A ___ , the second type of frequency measure used with dichotomous variables, is a ratio in which x is included in y
proportion
The third type of frequency measure used with dichotomous variables, ___ , is often a proportion, with an added dimension
rate = (# of cases or events during a given time period) / (population at risk during the same time period) x 10^n
It measures the occurrence of an event in a population over time.
The ___ rate expresses the probability or risk of illness in a population over a period of time.
incidence rate = (new cases occurring during a given period of time) / (pop. at risk during the same time period) x 10^n
___ rate, is the proportion of persons in a population who have a particular disease or attribute at a specified point in time or over a specified period of time.
prevalence (presence of a disease) = (all new & pre-existing cases during a given time period) / (population during the same period of time) x 10^n
prevalence (of an attribute) = (persons having a particular attribute during a given time period) / (population during the same period of time) x 10^n
How much of a particular disease is present in a population at a single point in time.
Point prevalence
How much of a particular disease is present in a population over a longer period.
Period prevalence
Attack rate formula ?
A.R = (# of new cases among the population during the period) / (pop. at risk at the beginning of the period) x 100
Secondary attack rate formula?
S.A.R = (# of cases among contacts of primary cases during the period) / (total # of contacts) x 10^n
A ___ ___, or ___ ___, compares the risk of some health-related event such as disease or death in two groups.
risk ratio or or relative risk = (risk for grp. of primary interest) / (risk for comparison grp.) x 1
risk ratio of 1.0 indicates?
A risk ratio of 1.0 indicates identical risk in the two groups.
risk ratio greater than and less than 1.0 indicates?
A risk ratio greater than 1.0 indicates an increased risk for the numerator group, while a risk ratio less than 1.0 indicates a decreased risk for the numerator group.
“How much more likely”
Odds ratio formula?
Odds ratio (cross-product ratio) looks at increased odds of getting a disease with exposure to a risk factor versus non exposure to that factor .
OD = ad/bc
When the health outcome is uncommon, the ___ ___ provides a good approximation of the relative risk.
odds ratio
A ___ ___ is a measure of the frequency of occurrence of death in a defined population during a specified interval.
mortality rate = (deaths occurring during a given time period) / (size of pop. among which deaths occurred) x 10^n
case-fatality rate formula?
C-F rate= (# of cause specific deaths among the incident cases) / (# of incident cases) x 10^n
Case-fatality rate is a proportion and requires that the deaths in the numerator be limited to the cases in the denominator.
Specific rate formula?
SR = (all events in specified subpopulation) / (specified subpopulation) x multiplier
Adjusted rates?
- Rates calculated to minimize demographic differences between populations being compared.
- Adjustment improves the validity of the comparison.
eg.
- The rate of alcoholism and alcohol abuse is found to be higher among workers in an automobile assembly plant compared with same-age workers at a textile mill in the same city.
- Adjustment for gender differences is warranted.
