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Epidemiology > Measures of Association: Descriptive Studies > Flashcards

Measures of Association: Descriptive Studies Flashcards

1
Q

What is the equation we need to know with 3 terms, such that x=y×z? What is x, y, and z

A

P=IR×D

P=Prevalence

IR=Incidence Rate

D=Duration

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2
Q

Which type of disease frequency (P, CI, IR): Percentage of dental students who get gingivitis over the fall semester.

A

Cumulative Incidence

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3
Q

Which type of disease frequency (P, CI, IR): Percentage of dental students who have gingivitis on the first day of class.

A

Prevalence

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4
Q

Which type of Disease frequency (P, CI, IR): Number of new cases of gingivitis in a year per 100,000 person-years.

A

Incidence Rate

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5
Q

Which type of disease frequency (P, CI, IR): Percent of dental students with gingivitis among 200 dental students.

A

Prevalence

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6
Q

True or False: Only the population at risk contributes to the denominator of cumulative incidence.

A

True

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7
Q

True or False: When calculating the incidence rate of disease, it is necessary to follow subjects for the same amount of time.

A

False

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8
Q

True or False: If the incidence rate of a very serious disease is 75/100,000 person-years and the prevalence in the population is 25/100,000 years, then the average duration of this disease must be 3 years.

A

False

answer=⅓ year

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9
Q

What is index determinant(group)?

A
  • people w/characteristic
    • exposed group
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10
Q

What is reference determinant (Group)?

A
  • People w/o characteristic or contrasting level of characteristic or alternative characteristic
  • unexposed group
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11
Q

What is the purpose of measures of association?

A
  • compares disease frequency:
    • prevalence
    • cumulative incidence
    • Incidence rate
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12
Q

What are the 2 types of Measures of Association?

A
  • Relative Measure of Association:
    • Ratio b/w index(exposed) & reference (unexposed)
  • Absolute Measure of Association:
    • Difference b/w index & reference
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13
Q

Relative Measures of Association

A
  • oRatio b/w index vs reference groups
  • No Units
  • General Formula: RR=Re/Ro
  • Prevalence:
    • Prevalence Ratio:
      • PR=Pe/Po
  • Cumulative Incidence:
    • Risk Ratio: (ratio of CI)
      • RR=CIe/CIo
  • Incidence Rate
    • Rate Ratio:
      • RR=IRe/IRo
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14
Q

If RR=1….

A
  • No Association
    • b/w exposure & disease
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15
Q

If RR>1….

A
  • Exposure is associated with INCREASED frequency of disease
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16
Q

If RR<1…

A
  • exposure is associated with DECREASED frequency of disease
17
Q

Interpret RR=0.75

A
  • Subjects with X had 0.75 times the risk of developing Y compared to those without X……OR
  • subjects with X had 25% less risk of developing Y compared to those without X
18
Q

How do you calculate Excess relative Risk?

A

Excess Relative Risk=(RR-1)x 100%

19
Q

What incidence ratio corresponds to a 20% increased incidence rate in the exposed vs unexposed group?

A

1.2

Excess Relative Risk=(RR-1)x100%

20%=(x-1)x100%

.20=x-1

1.2=x

20
Q

What incidence ratio corresponds to a 200% increased incidence ratio rate in the exposed vs unexposed group?

A

3.0

Excess Relative Risk=(RR-1)x100%

+200%=(x-1)x100%

2=x-1

x=3.0

21
Q

What incidence rate ratio corresponds to a 43% decreased incidence rate in the exposed vs unexposed group?

A

0.57

Excess Relative Risk=(RR-1)x100%

  • 43%=(x-1)x100%
  • .43=x-1

x=0.57

22
Q

What is the excess RR if RR=7.43? and interpret

A
  • Excess RR=(RR-1) x100%
    • Excess RR=643%
  • 643% increased risk
23
Q

Absolute Measures of Association

A
  • Difference (not ratio)
  • No Units:
    • EXCEPT Incidence rate
  • General Formula: RD=RI-Rr
  • Prevalence
    • Prevalence Difference
      • PD=Pe-Po
  • Cumulative Incidence
    • Risk Difference
      • RD=CIe-CIo
  • Incidence Rate
    • Rate Difference
      • RD=IRe-IRo
      • Units=person-time<u>-1</u>
24
Q

Investigators used a longitudinal cohort study design to assess whether exclusive long-term pipe smoking was associated with the development of head and neck cancers. Among pipe smokers, 171 developed head/neck cancer over 155,086 person-years of follow-up. Among never smokers, 155 developed head and neck cancer over 620,344 person-years of follow-up

Based only on this information, which absolute measure of association can we calculate:

A

Incidence Rate Difference

=IRe/IRo

IR={#new casespopulation @risk}xtime

25
Q

How do Relative and Absolute Measures of Association Differ?

A
  • Both provide different information & perspectives
  • Absolute measure
    • Public Health Impact
  • Relative Measure
    • strength/magnitude of association
26
Q

What are the different types of descriptive studies?

A
  • Case Reports
  • Case Series
  • Ecologic Studies
  • Cross-sectional studies
27
Q

What are the different type of analytical studies?

A
  • Case-control study
  • Cohort study
28
Q

Case Reports

A
  • Descriptive Study of 1 person/case
29
Q

What are case reports useful for?

A
  • recognize & describe:
    • new diseases
    • new manifestations of old diseases
  • Detect drug side effects
  • Provide:
    • disease mechanism
    • information
  • help develop hypotheses
30
Q

What are the disadvantages of case reports

A
  • No comparison group
  • can’t be used for hypothesis testing
31
Q

Case Series

A
  • many studies on a specific type of case
    • group of people w/similar problem
32
Q

What are some strengths and weaknesses of case series?

A
  • Strengths:
    • Provide descriptive data on disease characteritics
  • Weakness:
    • no control group
      • can’t be used for hypothesis testing
33
Q

Ecological Studies

A
  • aka Correlational study
  • examines rate of disease in relation to prevalence of exposure
  • no individual-level info collected
  • population usually identified by:
    • place
      • (city, state, neighborhood, country)
    • time
    • or combo
  • exposure and outcome measured at population level
34
Q

Ecological Studies: Strengths & Weaknesses

A
  • Strengths:
    • quick & inexpensive
    • done on available data
    • good for early stage of knowledge
    • when you want to study ecologic relationships
    • Easy analysis when using correlation coefficient or linear regression
  • Weakness:
    • Ecological Fallacy
    • No control for confounding factors
    • Correlation does not imply cause relationship
35
Q

Cross-Sectional Studies

A
  • study/survey that examines relationship b/w exposure status and disease status at one point in time (SNAP SHOT)
    • Exposure & disease are measured in same individual
  • Measures exposure prevalence vs disease prevalence
  • individual level data (unlike ecologic)

Epidemiology (6 decks)

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