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24 Cards in this Set
- Front
- Back
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What are the two types of incidence?
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Cumulative and person-time
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What is cumulative incidence also known as?
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Risk
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How do you calculate cumulative incidence?
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Number of new cases of a disease occurring in a defined period of time
/ Number of people in the population at the beginning of the period |
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What does cumulative incidence measure?
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How many new cases of a condition there are in a defined at-risk population over a specified period of time.
Requires a follow up study (cohort) |
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What does cumulative incidence not give?
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Information about how each person's time at risk varies over the time period
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How do you calculate person-time incidence?
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Number of new cases of a disease occurring in a defined period of time
/ person-time risk |
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How is person-time incidence different from cumulative incidence?
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The at-risk population is measured more accurately as it takes into account the fact that the people may drop out, migrate or die, or may only be intermittently exposed
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Which is more accurate: Cumulative incidence or person-time incidence?
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Person-time (think why!)
However it does require more resources and expenses. |
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When is the only time person-time incidence is not more accurate than cumulative incidence?
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When the population remains completely stable - not common in epidemiological studies!
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What is a 'person-year'?
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One person being at risk of the outcome being measured for one year.
One person being at risk for six months would be half a person year |
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How do you calculate 'person-year'?
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Multiply each person by time at risk the sum them all together.
This becomes the denominator |
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How would person-time incidence be expressed as a title?
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'The incidence of HIV in Uganda is x per 100,000 person-years.
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What is the variance of person-year called pack-year?
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A pack year takes into account of how much exposure a person has to a particular factor.
E.g. 1 pack of cigarettes per day for 40 years = 40 pack-years |
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What are the two types of prevalence?
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Point prevalence and period prevalence
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What is point prevalence?
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The number of existing cases of disease at one point in time
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How do you calculate point prevalence?
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Number of existing cases of a disease at one point in time
/ Population defined at the midpoint of the period |
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What is period prevalence?
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The number of existing cases of disease during a defined period of time
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Point prevalence includes people who were ill WAY before period of time
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Therefore PP is higher than
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How do you calculate period prevalence?
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Number of existing cases of a disease during a defined period
/ Population defined at the midpoint of the period |
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Point prevalence includes people who were ill way before that period of time.
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.
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Over any given time, period prevalence is greater than _________. Because
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incidence. Because period prevalence includes people who were ill way before the time, and the people presently ill.
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Prevalence is typically expressed as...
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...a percentage or number per 1000
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Why measure prevalence? (3)
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Used to find out how much of a disease burden there is on the population
Help in planning health services. See whether a condition is getting more or less common |
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Why is the rate ratio calculated?
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Calculated to compare the ratio of events occurring at any given point in time.
Rate Ratio = Incidence Rate 1/Incidence Rate 2 |
