Lecture 4: Epidemiological Risk Flashcards by Grace Johnson

What is a case?

A set of standard criteria for classification whether a person has a particular disease, syndrome or other health condition

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When comparing 2 populations with regards to a disease or exposure, what must you do?

use precise valid measures of disease frequency: point prevalence, period prevalence, cumulative incidence, incidence density
two populations must be distinct in location or time or exposure
apply statistical tests to these measures to see if any difference is likely to have occurred by chance

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What is a contingency table?

A 2x2 table

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What are the characteristics of a contingency table?

no fixed convention
advantage if set up the same way all the time
put exposure groups in rows with left row labels
put exposed (or most exposed) groups on the top row

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What is a risk?

Probability of an outcome

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What is a probability?

Likelihood of an event in relation to all possible events

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What is an association?

Correlation between exposure and outcome

N.B. CORRELATION DOES NOT IMPLY CAUSATION

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How can the strength of association between a putative Risk Factor and an outcome be measured?

Relative Risk - RR
Odds Ratio - OR
Attributable Risk - AR 
Population Attributable Risk - PAR
Absolute Risk - AR
Absolute Risk Reduction - ARR
Relative Risk Reduction - RRR
Number Needed to Treat - NNT

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What is the formula for Absolute Risk (AR) aka Incidence Risk (IR)?

n of new cases in specific T
AR= IR = ——————————————————-
N of individuals at risk in same T

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What are synonyms for Absolute Risk (AR)?

Incidence Rick (IR)
Cumulative incidence
Incidence

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What is the Relative Risk (RR)?

compares the incidence or risk of an event among those with a specific exposure with those who were not exposed

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What is the formula for Relative Risk (RR)?

Incidence Risk in the exposed
RR= ———————————————————-
Incidence Risk in the unexposed

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What does it mean if RR> 1

Positive association

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What does it mean if RR <1?

Negative association

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What is a synonyms for Relative Risk?

Risk Ratio

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When do we calculate Odds?

Only in case control studies

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What is an odds of an event?

Is the ratio of the probability that the event WILL occur to the probability that the event will NOT occur

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What is the formula for Odds of event?

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N of events
Odds of event= ——————————————————
Tot N of non events - N of events

   Or

                           P of events  Odds of event= ———————————
                           P of non events

What do you use toco late the Odds of Disease in individual with a certain exposure with the Odds of Disease in individuals who do not share the exposure?

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Odds ratio

What is the formula for Odds of disease?

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N of individuals with disease
Odds of disease=_______________________________
N of individuals without disease

What is the formula for Odds ratio (OR)?

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Odds of disease in exposed individuals
Odds ratio= ______________________________________
Odds of disease in unexposed individuals

What does OR stand for?

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Odds Ratio

What does OR<1 indicate?

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Exposure reduces disease risk

What does OR=1 indicate?

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Particular exposure is not a risk factor

What does OR >1 indicate ?

Exposure increases disease risk = exposure is a risk factor

When is OR a good approximation of RR?

When the “cases” studied are representative of all people with the disease in the population from which the cases were drawn When the “controls” studied are representative of all people without the disease in the population from which the cases were drawn When the disease being studied is uncommon within the population of study (low incidence rate: less than 5%)

What is Attributable Risk (AR) ?

measure of excess risk that is attributed to the exposure

What is the formula for Attributable Risk (AR)?

AR = Incidence Risk in exposed - Incidence Risk in unexposed AR= IR exposed - IR unexposed ( x 100 for percentages)

What is the Population attributable risk rate (PAR)?

is the risk in the total study population that is attributable to the presence of the exposure. The PAR depends upon the prevalence of the exposure in the study population.

What is the formula for PAR%?

PAR % = (I in whole pop - I non exposed) / I total. X 100 n of unexposed & no disease I in whole pop= _____________________________ Tot n of population n of non exposed with disease I non exposed = ________________________________ n of non exposed with disease + n of non exposed without disease

What are the formulas for PAR (population attributable Risk)?

PAR= I whole pop - I unexposed PAR= AR X proportion of population exposed = AR X n exposed __________ Tot population

What is Relative Risk Ratio (RRR)?

the extent to which the risk of a poor outcome is reduced by an intervention. An estimate of the number of people spared the consequences of an exposure that has been eliminated or controlled, expressed as a proportion of the number who would have been affected.

What is Absolute Risk Reduction (ARR)?

The amount by which the risk of a disease is reduced by control of a particular exposure.

What is the formula for Relative Risk Reduction (RRR)?

RRR= 1- RR (relative risk or risk ratio) IR unexposed = 1- ________________ IR exposed

What’s the formula for ARR (Absolute risk ratio)?

ARR= I control (placebo) - I intervention (exposed) | (%) (%) (%)

What is the Number Needed to Treat (NNT)?

N needed to treat to save one life

What is the formula for NNT (Number needed to treat) ?

1 NNT = ___________ X100 for % ARR(Absolute risk reduction) 1 = ______________ I control - I intervention (exposed)

Absolute Risk measures the risk or likelihood of an outcome within a specific population and a specific time period. True or false

True

Risk Ratios cannot be used to compare the likelihood of events in different groups, when we have access to incidence data. True or false?

False, it can

Odds Ratios are useful for comparison of exposures within different outcome groups, when we cannot calculate incidence. True or false?

True

Attributable Risk is a measure of excess disease or mortality, linked to an exposure or risk factor. True or false

True

What is the term used to describe the excess morbidity or mortality associated with an exposure Absolute risk Attributable risk Relative risk ratio

Attributable Risk

A study reports the absolute risk reduction of a cardiovascular event in those taking a statin is 4% over 10 years. What is the best estimate for the Number Needed to Treat (NNT) over 10 years to prevent one cardiovascular event? 10 25 40 55 70

Which item best explains why it would it be wrong to tell a patient "Your relative risk for heart disease is about 4.0"?. Single choice. Applying population-based research results to individuals is invalid Such specific numbers should not be given to patients There is no indication to which group they are being compared They might become depressed with this news They may have other risk factors for heart disease

There is no indication to which group they are being compared

Lecture 4: Epidemiological Risk Flashcards

(44 cards)