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31 Cards in this Set

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Define: The existing cases of disease at a specific point in time or during a specified period of time.
Prevalence
What is the numerator of prevalence?
Number of cases of disease
What is the denominator of prevalence
Number in population at a specified time point
What are the three types of prevalence?
Point, period and lifetime
Define: "Snapshot" view of the amount of disease in a population at a single point in time
Point prevalence
Define: Amount of disease in a population during a specified period of time
Period prevalence
point prevalence (at interval beginning) + incidence (new cases) = ________________
Period prevalence
Define: Perviod prevalence rate in which the period studeid is the whole of the subject's life
Lifetime prevalence
True/False: Point prevalence includes dead patients in the denominator.
False. They are removed from the population
What are the three uses of prevalence?
Asses public health impact of a specific disease on a community; Obtain periodic estimates of disease occurrence to track changes; Plan allocated health resources
List three limitations of prevalence.
Impact of survivor patients; change in incidence is not accounted for; prevalence does NOT measure risk
What type of information is measured in a cohort study?
Incidence
What type of information is measured in a cross-sectional study?
Prevalence
How do incidence and prevalence differ in terms of time?
Incidence is a period of time; Prevalence is for a period of time
What is the relationship between prevalence and incidence?
Prevalence = incidence * the average duration of the disease
How do incidence and prevalence differ in their denominator?
Incidence has all susceptible people present at the beginning of the period; Prevalence has all people examined including cases and noncases
How do incidence and prevalence differ in their numerator?
Incidence has all new cases occuring during a period of time among a gorup initially free of disease; Prevalence has all cases counted on a single survey\
List two assumptions associated with prevalence?
Incidence of the disease is constant over time; duration of the disease has been constant over time (steady state)
What does the prevalence ratio compare?
The prevalence between two populations
What are two distinct advantages of cross-sectional design?
1. provides good measure of disease prevalence 2. Can be quick, easy and inexpensive
What is one distinct disadvantages of cross-sectional design?
1. Measurement of disease and exposure status occurs at the same time. 2. Cannot determine disease incidence
A cohort study traces from __________ to ______________ as opposed to a case-control study traces from _____________ to _______________.
Exposure to Outcome; Outcome to Exposure
Why would we use a case-control study instead of a cohort study?
More efficient (narrower subject pool); faster (no need to wait from exposure to effect)
How are study subjects selected in a case-control study?
Subjected selected on the basis of disease status. Presence of disease = case; Absence of disease = control
Besides selecting subjects based on disease status what also needs to be done in a case-control study?
Exposure history of 'cases' compared to exposure history of 'controls'
What are two requirements for the selection of a control group in a case-control study?
Free of disease at time of study; must have had opportunity for both exposure and disease
What are the two types of biases for a Case-Control studies?
Selection, information
Define: A type of bias based on how subjects get into the study.
Selection bias (Detection, referral, nonresponse, self-selection, inappropriate comparison group)
Define: A type of bias based on after selection, exposure data
Information bias (recall, interviewer/abstractor, data collection, prevarication)
True/False: You calculate risk in a case-control study.
False, you estimate risk in a case-control study. You can NOT calculate risk in a case-control study.
Can you get incidence from a case-control study?
No. You cannot get incidence from a case control study. (This is also why you can't calculate relative risk)