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PPGH > 4. Health information intro > Flashcards

4. Health information intro Flashcards

1
Q

what is EPIDEMIOLOGY the study of

A

the study of the DISTRIBUTION and DETERMINANTS of DISEASE FREQUENCY in HUMAN populations
and the APPLICATION of this study to control health problems

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2
Q

EPIDEMIOLOGY 5 GOALS

A
  1. Identify the CAUSES of disease (aetiology)
  2. Determine the EXTENT/BURDEN of disease (assess healthcare needs and plan services)
  3. study the NATURAL HISTORY of disease (prognosis)
  4. Evaluate EFFECTIVENESS of interventions (prevention and treatment)
  5. Develop PUBLIC POLICY
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3
Q

4 components of MEASURING DISEASE FREQUENCY

A
  1. POPULATION (which group of people)
  2. NUMBER OF CASES (numerator)
  3. SIZE OF POPULATION (denominator)
  4. MEASURE of TIME
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4
Q

what is a POPULATION

A

the base group from which we count disease frequency

Group of people with a COMMON CHARACTERISTIC
eg
- place of residence
- gender, age
- use of hospital services (catchment population)
- life event (ie surgical procedure, giving birth)

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5
Q

what are the 2 Types of POPULATION and what do they mean

A
  • FIXED
    membership based on an EVENT and is PERMANENT
    eg hiroshima atomic bomb survivors
  • DYNAMIC (open)
    membership based on a CONDITION and is TRANSIENT
    eg. residents of Liverpool, hospital patients
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6
Q

NUMBER OF CASES is the NUMERATOR for all measures of frequency.
what are the PROBLEMS with NUMERATORS:

A
  1. WHO has the disease? (CASE DEFINITION)
    - Symptoms; subjective, reported by patient
    - Signs; objective, observed by clinician
    - Tests
  2. HOW do we find the cases? (DISEASE ASCERTAINMENT)
    - Routinely collected data
    - Specially commissioned data collections

different criteria used to define a case can give different results

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7
Q

SIZE OF POPULATION is the

A

DENOMINATOR for all measures

FULL or SAMPLE of population

necessary for COMPARISON of disease across populations

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8
Q

what is NECESSARY for ALL measures of disease frequency

A

TIME

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9
Q

MEASURE OF TIME
how can DISEASE OCCURANCE be measured

A
  • at SINGLE POINT in time
  • OVER a PERIOD of time
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10
Q

what is RATIO, PROPORTION and RATE

A

RATIO : division of two UNRELATED numbers

PROPORTION: division of two RELATED numbers
numerator is a SUBSET of denominator
expressed as %

RATE: division of two numbers
TIME is ALWAYS part of the DENOMINATOR

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11
Q

what is PREVALENCE and what is the calculation

A

EXISTING CASES

PROPORTION of population who have the disease

PREVALENCE = EXISTING CASES / TOTAL POPULATION

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12
Q

how is TIME in PREVALENCE

A
  • POINT : at a SINGLE point in time (MOST common) or
  • Period: at any time during a period

relevant time does not appear in formula but MUST BE STATED using words

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13
Q

what is INCIDENCE

A

NEW CASES of disease
during a SPECIFIED TIME PERIOD

  • DENOMINATOR includes POPULATION AT RISK (initially disease free)
  • involves TRANSITION from health to disease,
    TIME MUST PASS
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14
Q

what does the DENOMINATOR for INCIDENCE (New cases) include

A

the POPULATION AT RISK

  • excludes people who already have the disease or are immune
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15
Q

what does the DENOMINATOR for INCIDENCE (New cases) include

A

the POPULATION AT RISK

  • EXCLUDES people who already HAVE the DISEASE or are IMMUNE

eg post-natal depression population at risk is females that give birth,
prostate cancer - all adult males who have not removed their prostate

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16
Q

how are PREVALENCE STUDIES vs INCIDENCE STUDIES measured

A
  • Prevalence studies: CROSS-SECTIONAL
    people are studied for the presence of a condition at a ‘cross-section’ of time
    also called SURVEY if the main measurement is a questionnaire
  • Incidence studies: COHORT
    a sample of people FREE of the OUTCOME of interest is identified and observed OVER TIME to see whether an outcome event occurs
17
Q

how TIME is incorporated is different in INCIDENCE:
(2 types)

A
  • CUMULATIVE INCIDENCE
    Time is DESCRIBED in WORDS along with the number
  • INCIDENCE RATE
    Time is an intrinsic part of the DENOMINATOR
18
Q

what is CUMULATIVE INCIDENCE and what is the calculation

A

aka RISK

proportion of a population AT RISK that develops disease over a specified time period

CUMULATIVE INCIDENCE =
NO. NEW CASES during time period /
NO. POPULATION AT RISK at START of time period

time must be stated in words

19
Q

PROBLEMS with CUMULATIVE INCIDENCE

A

ASSUMES ALL PEOPLE in the study have been followed for the ENTIRE TIME PERIOD
(population could have changed by some moving away or death from other causes)

NOT a good measure in a DYNAMIC POPULATION or in a FIXED POPULATION that LOSES MEMBERS over time

20
Q

what does INCIDENCE RATE measure and what is the calculation

A

measures SPEED at which NEW CASES of disease occur

INCIDENCE RATE =
No. NEW CASES during time period /
TOTAL PERSON-TIME of observation in POPULATION AT RISK

Unit of denominator is ‘PERSON TIME’

21
Q

What is PERSON-TIME

A

counting the AMOUNT OF TIME people were AT RISK for (instead of counting people at risk)

when someone develops DISEASE they are no longer ‘at risk’ so NO LONGER contribute PERSON-TIME

each person contributes different amounts of person-time to the denominator

DENOMINATOR for INCIDENCE RATE

22
Q

HIGH PREVALENCE may result from

A
  • HIGH INCIDENCE (new cases)
  • LONG DISEASE DURATION
23
Q

RELATIONSHIP between PREVALENCE and INCIDENCE

A

PREVALENCE approx =
INCIDENCE RATE X AVERAGE DURATION

24
Q

the EPIDEMIOLOGIST’S BATHTUB

A

flow of water from tap: INCIDENCE
tub of water: PREVALENCE
flow of water through drain: DEATH (MORTALITY)
evaporation of water: RECOVERY or EMIGRATION

25
Q

what is MORTALITY RATE and how to calculate

A

INCIDENCE OF DEATH

MORTALITY RATE =
TOTAL NUMBER OF DEATHS /
TOTAL POPULATION AT RISK OF DEATH in the same period

eg still births mortality rate = stillbirths / live births and still births

(denominator: those who have disease and those who don’t)

(technically a proportion)

26
Q

why look at mortality?

A
  • Reliable data
  • Deaths classified according to standardised rules
  • Index of Severity of disease
  • Easier to obtain than Incidence data
  • Proxy (representative) for incidence (when disease is fatal and has short duration)
27
Q

time scale for Perinatal, Neonatal, Post-Neonatal and Infant MORTALITY

A

Perinatal: 28 weeks gestation - 7 days after birth

Neonatal: birth - 28 days

Post-Neonatal: 28 days - 1 year

Infant mortality: birth - 1 year

28
Q

a study that compares different populations is called

A

ECOLOGICAL STUDY

29
Q

what is CASE FATALITY RATE* (CFR)

A
  • What % of people with a DISEASE DIE within a certain time period after the disease was DIAGNOSED

CFR =
no. PEOPLE DYING during specified period AFTER DISEASE ONSET OR DIAGNOSIS /
No. PEOPLE DIAGNOSED with DISEASE

  • risk of death among those diagnosed
  • measure of disease severity

(technically a proportion)

30
Q

difference between MORTALITY RATE and CFR

A

mortality rate: denominator is entire population at risk (of disease/death)

CFR: denominator is only those DIAGNOSED with the disease

ie. population at risk = 15
people with disease = 5
death from disease = 2

CFR = 2/5 = 40%
MORTALITY rate = 2/15 = 13.3%
(cumulative incidence = 5/15 = 33%)

31
Q

what is LIFE EXPECTANCY

A

AVERAGE LENGTH OF TIME AN INDIVIDUAL IS EXPECTED TO LIVE
if TODAY’S AGE AND SEX-SPECIFIC MORTALITY RATES CONTINUE

  • can be calculated from any age, most common at birth
  • CANNOT be used to predict individual lifespan
32
Q

what is HEALTHY LIFE EXPECTANCY

A

AVERAGE LENGTH OF TIME A PERSON CAN EXPECT TO LIVE FREE OF DISEASE

combines measures of MORBIDITY with MORTALITY

33
Q

DATA SOURCE for MORTALITY

A

DEATH REGISTRATIONS (ONS)

34
Q

DATA SOURCES for MORBIDITY

A
  • Primary care
  • Secondary care
  • Notifications of infectious diseases & Surveillance
  • Disease registers
  • Population based Surveys
35
Q

CRITIERIA for the Quality and Utility of HEALTH DATA

A
  • NATURE of data
  • AVAILABILITY of data
  • COMPLETENESS of POPULATION COVERAGE
    representativeness,
    generalizability (external validity)
    thoroughness
  • STRENGTHS vs LIMITATIONS

PPGH (10 decks)

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