Epidemiology Flashcards
Prevalence
Number of EXISTING cases of an outcome at ONE POINT IN TIME
expressed as proportion or percentage
Incidence
Number of NEW cases of an outcome DURING A TIME INTERVAL
expressed as rate (denominator includes time component)
Risk
Probability of disease occurring in a disease-free population during a specified time period
Risk = N/P
N = new cases in defined period
P = population at risk
Rate
Probability of disease occurring in a disease-free population during the sum of individual follow up periods (person-time)
Rate = N/T
N = new cases in defined period
T = total person-time of follow-up
Relative Risk (RR)
RELATIVE change in risk/rate of outcome associated with exposure
RR = Re/Ru
Re= Risk/Rate among exposed
Ru = Risk/Rate among unexposed
Attributable Risk (AR)
ABSOLUTE change in risk/rate of outcome associated with exposure
AR = Re – Ru
Re= Risk/Rate among exposed
Ru = Risk/Rate among unexposed
Attributable Risk Percent (AR%)
AR% = [(Re – Ru) / Re ] * 100
Population Attributable Risk (PAR)
PAR = Rt – Ru Rt = Risk/Rate in whole population (both exposed and unexposed) Ru = Risk/Rate among unexposed
Population Attributable Risk Percent (PAR%)
PAR% = [ (Rt – Ru) / Rt ] * 100 Rt = Risk/Rate in whole population (both exposed and unexposed) Ru = Risk/Rate among unexposed
Bradford Hill Criteria for Causality
Temporal Relationship Strength Dose Relationship Consistency (multiple studies show same results) Plausibility (makes sense) Excludes Alternatives Experimental Evidence Specificity (lung cancer & smoking study) Coherence
Odds Ratio
Used for case control studies to approximate relative risk
OR = odds of exposure vs non exposure among cases / odds of exposure vs non exposure among controls
Hazard
Continuously updated instantaneous rate
Week 1, 10 die, hazard week 1 = 10/1000
Week 2, 15 die, hazard week 2 = 15/990
Relative Rate Reduction
Relative Rate Reduction = Rc / Ri
Rc = rate of outcome in control arm
Ri = rate of outcome in intervention arm
Absolute Rate Reduction
Absolute Rate Reduction = Rc – Ri
Rc = rate of outcome in control arm
Ri = rate of outcome in intervention arm
Number Needed To Treat
NNT = 1 / (absolute risk or rate reduction)
Defines number of people needed to undergo the intervention in order to prevent outcome in one person
PICOT
Population Intervention Comparator/Control Outcome Timing
Internal Validity
Extent to which the results of a study are valid (accurate, robust, sound and complete).
Statistical Significance
P-value < 0.05
Probability that the observed result arose from chance
Confidence Interval
Interval within there is 95% chance the true value lies
If null value is excluded result is statistically significant
External Validity
Extent to which the results of a study are applicable to a clinical scenario (using PICOT)
Systematic Review
Idenitify, appraise,select, synthesize
Focuses on single question
Well defined criteria
Highest NHMRC level of evidence
Meta-analysis
Statistical Aspect of systematic review
Derived (weighted-average) effect size
Increases power and answers other questions
Heterogeneity
Whether component studies are similar enough to be pooled
Diagnostic Test
Confirmation of disease (high pre-test probability of disease)
Screening test
Identify patients who may have disease (low pre-test probability of disease)
Sensitivity
True Positive / (True Positive + False Negative)
% of people with disease that test positive
Specificity
True Negative / (True Negative + False Positive)
% of people without disease that test negative
Positive Predictive Value
True Positive / (True Positive + False Positive)
% of positive tests that are truly positive
Dependant on prevalence of disease
Negative Predictive Value
True Negative / (True Negative + False Negative)
% of negative tests that are truly negative
Dependant on prevalence of disease
Likelihood Ratio of Positive Test
Sensitivity / (1 - Specificity)
Likelihood Ratio of Negative Test
(1 - Sensitivity) / Specificity)
Social Determinants of Health
- Social Gradient
- Stress
- Early Start
- Social Inclusion
- Work
- Unemployment
- Social Support
- Addiction
- Food
- Clean Transport
Observational Studies
case series, case reports ecological cross-sectional case-control cohort
Interventional Studies
clinical trials
Descriptive Studies
case series, case reports
ecological
cross-sectional
e.g. How common is coronary heart disease?
Analytical Studies
case-control
cohort
clinical trials
e.g. Does dyslypidaemia increase the risk of CHD?
Do lipid-lowering medications decrease the risk of CHD?
Cross Sectional Studies
Data collected via questionnaires, examinations, investigations Mostly descriptive (esp. PREVALENCE)
Case Control Studies
Comparison of PREVIOUS exposure between Cases (have outcome) and Controls (without outcome) Matched by confounders RETROSPECTIVE Useful for studying rare outcomes output: ODDS RATIO
Cohort Studies
LONGITUDINAL with FOLLOW-UP
collect INCIDENCE data
derive RELATIVE RISKS
Clinical Trials
LONGITUDINAL assess if INTERVENTION changes INCIDENCE outcomes: RR HR ARR NNT
Death Stats
1/5 deaths are children under 5
- communicable diseases account for 50%
- malnutrition underlying cause of 30%
- 37% of deaths are neonates (under 28 days)
out of every 10 deaths
- 6 non-communicable diseases
- 3 communicable, reproductive, nutritional
- 1 injury (males)
Leading causes of death
- Ischemic Heart Disease
- Cardiovascular Disease
- Infections / Parasitic
- Cancers
Millenium Development Goal 4
Reduce the under 5 mortality rate by 2/3rds by 2015
Leading Global Cause of DALYs
- Unipolar depressive disorders
- Hearing loss (adult onset)
- Alcohol use disorders
Leading global risk factors for mortality
- High Blood Pressure (13% of deaths)
- Childhood underweight (2million children)
- Unsafe water, sanitation, hygiene, indoor smoke (2million children)
- Unsafe sex
- Tobacco (1/8 deaths over 30)
- Obesity (7% of deaths globally)
Tobacco Control
Tobacco is a risk factor for 6 of the top 8 leading causes of death
Monitor tobacco use and prevention policies
Protect people from tobacco smoke (smoking bans)
Offer help to quit tobacco use (nicotine replacement)
Warn about the dangers of tobacco (packaging & adds)
Enforce bans on tobacco advertising
Raise taxes on tobacco (most effective)
Australia most expensive place to buy Marlboro
Tobacco use declining among teens (alcohol rising)
Lung cancer rates declining in males (females rising)
COPD death rates declining
CHD rates declining
400,000 deaths averted
Tobacco will kill approx 1billion people this century (due to smoking by pre-teens in south east asia and china WHO FCTC (framework convention on tobacco control) developed to combat worldwide tobacco smoking
Leading causes of Blindness and Vision Impairment
Blindness (Australia)
- Age Related Macular Degeneration (48%)
- Glaucoma (14%)
- Cataract (12%)
Vision Impairment (Australia)
- Refractive Error (62%)
- Cataract (14%)
- Age Related Macular Degeneration (10%)
Blindness (Worldwide)
- Cataract (39%)
- Refractive Errors (18%)
- Glaucoma (10%)
Indigenous Eye Health
Aboriginal kids born with better vision (1/5th vision loss c.f mainstream)
Blindness 6x more common in adults than mainstream
Low vision 3x more common
Primary causes
- Cataract (12x more common, 7 year wait for surgery)
- Refractive Errors (only 20% wear glasses)
- Trachoma (Surgery, Antibiotics, Facial cleanliness, Environmental improvements)
- Diabetes (only 20% have yearly eye exam)
94% of vision impairment avoidable with early intervention
