Formulas for Exam 1 Flashcards

1
Q

Cumulative Incidence

A

= Number of new cases of disease/ Number at-risk in population
*during specified time period

This estimates the probability (risk) that a person will develop disease during a specified time

PROPORTION expressed as a %

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2
Q

Attack rate

A

=Number of new cases of disease /Total population at risk

*for “limited” period of observation
NOT actually a rate, a fraction
For acute epidemics and outbreaks

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3
Q

Case-Fatality Rate

A

Case-Fatality Rate = Number of deaths from disease/
Number of cases of that disease
*in a specified time period

Another CI measure
NOT a rate but a fraction

Reflects severity of disease

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4
Q

Incidence Rate (IR)

A

IR = Number of new cases of disease/ Total at-risk person-time of observation

*during time period

TRUE RATE

“Incidence density” another name

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5
Q

Mortality Rate

A

Mortality Rate = Total number of deaths/
Total person-time of follow-up

mid-year population rate of dying during a time period

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6
Q

Mortality (cumulative incidence of death)

A

Mortality = Total number of deaths/
Total population during time of relevance

NOT a rate but a CI of dying
RISK

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7
Q

IR and CI relationtionship

A

CI ≈ IR * Time Period

*for CI < 10%

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8
Q

Prevalence

A

P = Number of existing cases of disease / Total number of people in population at that time

A proportion

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9
Q

Survival

A

Survival = Number still alive by time(X) / Total number with disease at start of follow-up

not a rate

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10
Q

Birth defect rate

A

Birth defect “rate” = Number of children born with defects/ Total number of births

NOT a rate

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11
Q

Point prevalence and incidence prevalence relationship

A

time duration* IR = P / (1-P)

P ~ IR * D when P is <10%

The time duration is the average time that the disease lasts in the population (afterdiagnosis, before recovery, emigration or death)

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12
Q

Direct Adjustment Computation

A

Age-adjusted rate = (age-specific rate × weight)

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13
Q

Absolute measures (CI or Prevalence)

A
Prevalence or cumulative incidence 
(depending upon sampling)
= a/(a+b) among exposed
= c/(c+d) among unexposed
= (a+c)/(  a+b+c+d) among total sample
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14
Q

Absolute Measure (IR)

A

Incidence Rate:
= a/(PTexp) among exposed
= c/(PTunexp) among unexposed
= (a+c)/( PTtot) in total sample

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15
Q

Risk Difference “Attributable risk”

A

RD = Rexp− Runexp

For CI: RD = CID = CIexp- CIunexp= [a / (a+b)] – [c / (c+d)]
For IR: RD = IRD = IRexp- IRunexp= [a / PTexp] – [c / PTunexp]
For Prev: RD = PD = Pexp - Punexp= [a / (a+b)] – [c / (c+d)]

excesss risk in the exposed group

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16
Q

For Cumulative Incidence and Prevalence

A

Excess Number of Cases = RD × Number Exposed

17
Q

For Incidence Rate

A

Excess Number of Cases = RD ×Person-Years Exposed

Excess number of cases= APe x number cases exposed

18
Q

Population Risk Difference (PRD)

A
PRD = Rtot− Runexp
PRD =   RD × Pexptot

impact of exposure on the total pop

19
Q

Attributable Proportion Among exposed

A

APexp = Rexp−Runexp/ = RD/ Rexp
Rexp
Also called etiologic fraction, attributable risk percent, attributable risk percent among exposed

no units

20
Q

Attributable proportion among total population

A

APtot=Rtot – Runexp/ = PRD/ Rtot

Rtot

21
Q

The Study of Epidemiology

A

The study of the distribution and determinants of disease frequency in human populations and the application of this study to control health problems.

22
Q

what is scientific about epi

A

the use of representative sampling of people, diseases and exposures to draw inferences about causation in general

23
Q

components of epidemiology

A
  1. eDistribution: Descriptive epi, person, place time, who, when, where
  2. Determinants: etiologic, causation, risk factors
  3. Frequency
24
Q

Distinguishing factor of epidemiology from medicine and public health

A

populations

25
Primary prevention
reducing risk or occurrence of disease in people who do not have disease
26
Secondary prevention:
prevent asymptomatic disease from becoming symptomatic (e.g., early diagnosis and prompt treatment), or preventing transmission of infectious diseases from cases to susceptible individuals
27
Tertiary prevention:
reduce damage of symptomatic disease, e.g., rehabilitation, halting progression and complications
28
Descriptive epidemiology
who what where and when NOT how
29
purpose of descriptive epi
1. clues about disease causation and prevention 2. assess and qualify the health status of a pop. 3. Allocate resources efficiently and target populations for disease prevention and health promotion efforts
30
Uses of descriptive epi
1. hypothesis generator 2. public health planning 3. Research: determining best prevention methods
31
Goals of measures of frequency
1. measure distribution of disease 2. measure burden 3. to compare between groups to asses disease determinants
32
Components of measures of frequency
1. count: number affected 2. source of population 3. time
33
types of populations
1. Fixed: membership is permanent | 2. Dynamic: membership is tansient
34
Most important determinant of mortality
Age
35
Another excess cases
Excess number of cases = Exposed cases -Runex x Total Exposed
36
Attributable proportion of the exposed (alt formula)
APexp= Excess cases / Exposed cases
37
Attributable proportion of the total pop (alt formula)
APtot= excess cases / total cases
38
Excess relative risk
ERR= 1- RR *100 expressed as a percent