Lecture 1. Measuring Disease Flashcards
What is the definition of epidemiology?
Epidemiology is the study of diseases in populations (emphasis on populations)
What does prognosis mean?
Outcome
What is a key indicator to see if someone is HIV positive or negative?
The CD4 lymphocyte count
What can we ask from an epidemiological study?
Diagnosis, prognosis
Determine the extent – quantify the incidence or prevalence of disease
The why behind the disease - identify the likely etiology and risk factors
What does etiology mean?
The cause of disease
What are risk factors?
Those that increase a persons risk to a disease
What questions are asked by taking an epidemiological approach?
Is there an association between exposure to a variable and development of disease in question?
Is this difference real? Why have they occurred?
What two ways can a disease be measured?
Ratio and Proportion
What is a ratio?
a/b
Relationship between two quantities, e.g. dilute this reagent 1:4 means for every 1 part reagent add 4 parts buffer
What is a proportion?
a/(a+b)
Specific type of ratio comparing to a whole
What is rate?
How fast the disease is occurring
What is a snapshot?
Expresses the relationship between an event and a defined population evaluated over a specified time period
What is incidence?
Number of new cases of a disease occurring in the population during a specified time period/number of people who are at risk of developing disease during that period of time
What two factors make up an incidence recording?
A rate and a proportion (e.g the proportion of women diagnosed with breast cancer this year)
What does the denominator of incidence represent?
The people at risk
What is prevalence?
Number of cases of disease in the population at a specified time/Number of people in the population at that time
What two factors make up a prevalence recording?
A snapshot and a proportion (e.g the proportion of women with breast cancer today)
Does incidence have units?
Yes, e.g people per year
Does prevalence have units?
No
What is point prevalence?
The amount of a variable at one point in time
Typical (e.g do you current have asthma?)
What is period prevalence?
The amount of a variable over a defined time period
e.g the number of women with breast cancer in 2014
What is the prevalence of a disease dependent on?
The incidence, i.e. how quickly new cases develop
How long the disease lasts due to deaths or recovery
What is incidence a measure of that prevalence is not?
Risk (gold standard when comparing diseases)
What is way of estimating incidence? (there is a relationship but the equation is not true)
Prevalence/Duration of infection (time)
What is a variable?
Something that we are interested in that varies
What is a response/dependent variable?
The variable that we expect to be influenced by other variables
What is a predictor/independent variable?
The variables that change our response variable
What is a risk factor?
A variable which is associated with an increase in a disease
What ways can associations between risk factors and disease incidence be measured?
Risk ratio (RR) = relative risk
Odds ratio (OR)
Attributable risk (AR)
Population Attributable risk (PAR)
Attributable Proportion
How can statistical association be measured?
Chi-square test (χ²)
How is the risk ratio (RR) calculated?
Risk of disease in exposed/risk of disease in unexposed
a/(a+b) / c/(c+d) = a/(a+b) x (c+d)/c
What does it mean when RR = 1?
Risk in exposed is equal to risk in non-exposed (no association)
What does it mean when RR > 1?
Risk in exposed is greater than risk in non-exposed (positive)
What does it mean when RR < 1?
Risk in exposed is less than risk in non-exposed (negative)
How is the odds ratio (OR) calculated?
Odds of disease in exposed/odds of disease in unexposed
a/b / c/d = ad/bc
What does it mean when OR = 1?
Odds in exposed is equal to odds in non-exposed (no association)
What does it mean when OR > 1?
Odds in exposed is greater than odds in non-exposed (positive)
What does it mean when OR < 1?
Odds in exposed is less than odds in non-exposed (negative)
What do RR and OR tell us?
How strong the association between disease and exposure
A measure of effect is useful to evaluate causality
What is attributable risk?
The amount of disease attributable to an exposure in those exposed
Sometimes reported as a proportion (e.g 200 of the 230/1000 cases of lung cancer are due to cigarette smoking)
How is attributable risk calculated?
Risk in exposed - risk in unexposed
a/(a+b) - c/(c+d)
Why is attributable risk useful?
Allows us to evaluate potential for prevention
What is population attributable risk (PAR)?
The amount of disease attributable to an exposure in the population
How is population attributable risk calculated?
Attributable risk x prevalence of exposure in population
What does PAR measure?
Potential impact of control measures in a population, and is relevant to decisions in public health
What is PAR useful for?
Determining allocation of resources
