SPHG 712 Unit 1 Test With
Complete Solution
Prevalence - ANSWER Definition:
- The proportion of the population living with a health condition at a specific
period or point in time
- Used when difficult to determine the onset of the health outcome or if the
disease has a long duration
Limitations:
- Tends to favor the inclusion of chronic diseases over acute ones
- Hard to infer causality because exposure and new outcomes are measured
simulatenously
Formulas:
- New + current cases/total study population at the point of inquiry
- alternatively: rate * duration
How to interpret:
- A population with a heart disease prevalence of 0.25 indicates that 25% of
the population is affected by heart disease at a specific moment in time.
Incidence - ANSWER The proportion of the population who developed the
health condition over the specific amount of time
Formulas:
,new cases / total at-risk study population at baseline
Cases - ANSWER Persons who experience the outcome of interest
Point prevalence - ANSWER The percentage of people in a given population
who have a given disorder at any particular point in time.
Period prevalence - ANSWER A measure of how many individuals were
affected by the disease during a specified time period.
Risk - ANSWER Definition:
- The number of new cases is divided by the total at-risk population at the
beginning of the follow-up period.
What does it measure?
- Measures of the probability of an unaffected individual developing a
specified health outcome over a given period of time.
Formula:
- Incident Cases/Population at-risk at start of the study
How to interpret:
- 0.x cases per person or XX cases per 100 or 1000 persons -> so a five-year
risk of 0.10 means that an individual at risk has a 10% chance of developing
the health outcome over a five-year period
What kind of studies use this measure?
- Prospective studies because the population at risk is easy to determine and
follow
- NOT case-control studies because the total population can not be
,determined, SO we use odds instead.
Also known as:
- incidence, cumulative incidence, or attack rate
Rate - ANSWER Definition:
- The proportion of the population who developed the health condition per
unit time at risk over the specified amount of follow-up time.
What does this measure?
- Measures how quickly the health outcome is occurring the population
Formula:
- Incident Cases/Total Person-time at-risk during the study period (usually
years)
How to interpret?
- A rate of 0.1 case/person-years indicates that on average, for every 10
person-years contributed, 1 new case of the health outcome will develop.
- Commonly multiplied by 1k or 10k person-years, and written as X cases per
1k or 10k person-years.
Also known as:
- incidence rate or incidence density
Note 1: Denominator of person-time-at-risk changes as persons originally at
risk develops the health outcome during the observation period and are
moved from the denominator into the numerator
, Total Person-time at-risk - ANSWER Sum total of time all individuals remain
in the study without developing the outcome of interest.
Time without developing outcome interest = time where the individuals are
still at risk of developing the risk
Note: as it can be difficult to determine the exact time when a person
becomes a case, investigators commonly will use the midpoint of the interval
between being disease-free and becoming a case as the "onset of case"
Odds - ANSWER Definition:
- ratio of cases to non-cases
Formula:
- Cases (can be either incident or prevalent)/non-cases
What kind of studies use this measure?
- Case-control studies, where we have a group of individuals with the health
outcome and a group of individuals without the health outcome of interest
that are selected
Two-by-Two Tables - ANSWER generally used to organize the data from a
study
Exposed + Diseased = A
Exposed + No Disease = B
Unexposed + Diseased = C
Unexposed + No Disease = D
SO:
Complete Solution
Prevalence - ANSWER Definition:
- The proportion of the population living with a health condition at a specific
period or point in time
- Used when difficult to determine the onset of the health outcome or if the
disease has a long duration
Limitations:
- Tends to favor the inclusion of chronic diseases over acute ones
- Hard to infer causality because exposure and new outcomes are measured
simulatenously
Formulas:
- New + current cases/total study population at the point of inquiry
- alternatively: rate * duration
How to interpret:
- A population with a heart disease prevalence of 0.25 indicates that 25% of
the population is affected by heart disease at a specific moment in time.
Incidence - ANSWER The proportion of the population who developed the
health condition over the specific amount of time
Formulas:
,new cases / total at-risk study population at baseline
Cases - ANSWER Persons who experience the outcome of interest
Point prevalence - ANSWER The percentage of people in a given population
who have a given disorder at any particular point in time.
Period prevalence - ANSWER A measure of how many individuals were
affected by the disease during a specified time period.
Risk - ANSWER Definition:
- The number of new cases is divided by the total at-risk population at the
beginning of the follow-up period.
What does it measure?
- Measures of the probability of an unaffected individual developing a
specified health outcome over a given period of time.
Formula:
- Incident Cases/Population at-risk at start of the study
How to interpret:
- 0.x cases per person or XX cases per 100 or 1000 persons -> so a five-year
risk of 0.10 means that an individual at risk has a 10% chance of developing
the health outcome over a five-year period
What kind of studies use this measure?
- Prospective studies because the population at risk is easy to determine and
follow
- NOT case-control studies because the total population can not be
,determined, SO we use odds instead.
Also known as:
- incidence, cumulative incidence, or attack rate
Rate - ANSWER Definition:
- The proportion of the population who developed the health condition per
unit time at risk over the specified amount of follow-up time.
What does this measure?
- Measures how quickly the health outcome is occurring the population
Formula:
- Incident Cases/Total Person-time at-risk during the study period (usually
years)
How to interpret?
- A rate of 0.1 case/person-years indicates that on average, for every 10
person-years contributed, 1 new case of the health outcome will develop.
- Commonly multiplied by 1k or 10k person-years, and written as X cases per
1k or 10k person-years.
Also known as:
- incidence rate or incidence density
Note 1: Denominator of person-time-at-risk changes as persons originally at
risk develops the health outcome during the observation period and are
moved from the denominator into the numerator
, Total Person-time at-risk - ANSWER Sum total of time all individuals remain
in the study without developing the outcome of interest.
Time without developing outcome interest = time where the individuals are
still at risk of developing the risk
Note: as it can be difficult to determine the exact time when a person
becomes a case, investigators commonly will use the midpoint of the interval
between being disease-free and becoming a case as the "onset of case"
Odds - ANSWER Definition:
- ratio of cases to non-cases
Formula:
- Cases (can be either incident or prevalent)/non-cases
What kind of studies use this measure?
- Case-control studies, where we have a group of individuals with the health
outcome and a group of individuals without the health outcome of interest
that are selected
Two-by-Two Tables - ANSWER generally used to organize the data from a
study
Exposed + Diseased = A
Exposed + No Disease = B
Unexposed + Diseased = C
Unexposed + No Disease = D
SO:
