Introduction Flashcards
what is epidemiology?
study of patterns causes and effects of health and disease in defined populations
it informs our public health, policy, evidence-based practice - identifying risk factors and interventions for prevention
why is epidemiology important?
understanding risks, used for designing public health interventions, underpins much of evidence-based medicine
outline cholera
John snow
higher death rates in 2 areas supplied by same water company
identified pump on Broad street as cause of epidemic
used chlorine to clean handle and ended the outbreak
outline the smoking ‘british doctors study’
prospective cohort study by medical research council
1951- wrote to UK physicians
40,000 responded, males
statistical evidence linking smoking to lung cancer
outline AIDS epidemic 1980s
cohort study 1993 Schechter
followed 715 gay men for 8.6 years
all 126 AIDS cases only occurred in those 365 individuals with pre-existing HIV-1 antibody and CD4 counts fell - changed beliefs on aetiology
HIV-1 is involved in AIDS pathogenesis
outline the Northern Region Young Persons Malignant Disease Registry
cancer registry
all cases of cancer diagnosed in those 0-24 years from 1968-today
population based - cases from defined geographical region and time
what has the northern region young persons maligant disease registry shown
improved survival for children and young people with cancer
seasonal variation - indicates a role for environmental factors in aetiology
socio-economic disparities in survival
how can we measure disease frequency
incidence rate
prevalence rate
mortality rate
relative risk
rate ratio
standardised morbidity ratio
odds ratio
what are the 4 main study designs
case-control studies
cohort studies
cross-sectional studies
ecological studies
what is the definition of bias
any systematic error in epidemiological study resulting in incorrect estimate of association between exposure and risk of disease
selection bias/misclassification bias
what is the definiton of confounding
function of the complex interrelationships between various exposures and disease
what is genetic epidemiology
study of role of genetic factors in determining health and disease in families and populations
gene-environment interactions
what are the types of genetic study design
familial aggregation studies
segregation studies
linkage studies
association studies
what are family aggregation studies
find out if there is a genetic component and what the relative contributions of the genes and environment are
what are segregation studies in genetic epidemiology
find out the pattern of inheritance of disease (dominant or recessive)
what are linkage studies in genetic epidemiology
find out which part of the chromosome the disease gene is located
what are association studies within genetic epidemiology
find out which allele of which gene is associated with the disease
what is the recent thing in genetic epidemiology
genome-wide association studies - lead to the discovery of many genetic polymorphisms that influence risk of developing common diseases
what is life course epidemiology
study of antecedant exposures and later health outcomes
take into account pathways between the two and evolution of health disorders over time
used to study long term effects on chronic disease and risk of exposure during gestation, childhood, adolescence and later life
what is perinatal epidemiology
period immediately before or after birth
congenital anomalies in children - aetiology and survival
reproductive loss
what is the prevalence of cancer
approx 1 in 2 people will be diagnosed with cancer at some point in their lives
risk increases in people 50+
what diseases does obesity increase the likelihood of
BMI > 30
heart disease
type 2 diabetes
obstructive sleep apnea
certain cancers
osteoarthiritis
outline the Newcastle 85+ study
out of those ages 85+ years no one was disease free and on average each person has 4-5 conditions
what are the methods used to investigate infections
outbreak investigation
disease surveillance
case-control studies
cohort studies
molecular epidemiology
vaccine assessments
what is the definition of health inequality
differences in health status or distribution of health determinants between different populations
what did the study of melanoma by McNally 2014 show
incidence and survival in young people in northern england
found increased risk of melanoma was linked to greater affluence but worse survival associated with living in a more deprived area
what is incidence rate used to measure
measure and compare disease frequency in populations
good because rates adjust for population size
what is the definition of incidence rate
number of new cases of a specified disease per population at risk in a given time period
how is incidence rate calculated
(new cases occuring in given time period) / (population at risk during same time period)
what should the numerator of the incidence rate equation not include
cases occurred/diagnosed earlier or later than the given time period
what does the denominator of the incidence rate equation represent
the population from which the cases in the numerator arose from
what is incidence rate specific for
age and sex
females and males are calculated separately
age calculated by 5 year group
what must be ensured when calculating age/sex specific incidence
complete ascertainment of cases for a prescribed geographical area e.g country, county, district, ward
what is the crude incidence rate
calculated as total number of cases / total population in the period
what does the crude incidence rate not take into account?
the age structure of the population and cannot be used for comparison with other populations/countries
what is an example of when crude incidence rate did not work
2 australian health surveys examined circulatory system health problems in general population and indigenous population in each age group over 24 years, indigenous had higher rates but crude incidence showed general as higher because the median age of indigenous was 21 and median age of general was 37
how do we overcome the problem of comparing populations with different age structures?
weighting
rates are weighted to a standard population e.g WHO
AGE-STANDARDISED INCIDENCE RATE
so how is age standardised incidence rate calculated
summary of individual age-specific rates using external population standard
d(i) / y (i) = age specific rate for i category
what is prevalence
frequency of existing cases
how much of a particular disease is present in a defined population
so what is the difference between the numerators of incidence and prevalence
indice numerator is new cases in given time period
prevalence numerator is all cases present during given time period irrespective of when disease started
both new and old cases
what is the equation for prevalence rate
(persons with given disease/condition during specified time period) / (population during same time period)
what is mortality rate
probability/risk of dying in population over a period of time
frequency with which new death occurs in population over period of time
what are some other types of mortality rate
perinatal mortality rate - neonatal death and stillbirth
maternal mortality rate - 15-44yrs
infant mortality rate -<1yr
child mortality rate <5 yrs
what is relative risk
measure of disease frequency by calculating ratios - risk ratio and rate ratio
measures the strength of an association
what is the risk ratio equation
risk (cumulative incidence) in exposed group / risk in unexposed group
what is rate ratio equation
incidence rate in exposed group / incidence rate in unexposed group
what is the odds ratio
odds of disease in exposed group / odds of disease in unexposed group
what does the rate ratio do
compares 2 groups in terms or incidence/mortality rate
the two groups differ by demographic or exposure
rate ratio = rate for group of interest / rate for comparison group
what does a rate ratio of 1 mean
identical risk in the 2 groups
what does a rate ratio of > 1 mean
increased risk for numerator group
what does a rate ratio of < 1 mean
increased risk for denominator group
what is the odds ratio definition
estimate of risk from case-control studies
measure of association - quantifies relationship between exposure and health outcome from comparative study (case-control study)
what is the equation for odds ratio - case control studies
odd ratio = (a x d) / (b x c)
what is the abcd of the odds ratio equation
a = ppl with disease and exposure of interest
b = ppl without disease but with exposure of interest
c = ppl with disease but without exposure of interest
d = ppl without disease or exposure of interest
and is a+c and what is B+D
ac = cases
bd = controls
what is the standard mortality ratio equation
SMR = observed cases / expected cases x 100
outline standard morbidity ratio
can be morbidity mortality or incidence
quantifies increase or decrease in those relative to general population
what is the p value
measure of statistical significance
probability of an event occurring due to chance alone
higher p value = higher probability the event can be explained by chance
from 0.0 to 1.0
cut offs 0.05/0.01
