What measures are used to determine the strength of the relationship between an exposure and an
outcome? Effect of an exposure in causing an outcome? - Measures of association --> relative risk (RR),
odds ratio (OR), incidence rate ratio (IRR)
Measures of effect -->
i) in an exposed group: risk difference (RD), attributable proportion exposed
ii) in a population: population attributable risk (PAR), population attributable fraction (PAF)
What is relative risk? How is it calculated and interpreted? - Relative risk is a ratio of 2 probabilities and
is calculated as follows:
RR = P(D+|E+)/P(D+/E-)
An RR> 1 means that the exposed group is more likely to show the outcome than the non-exposed
group while an RR<1 means the exposed group is less likely than the non-exposed group to show the
outcome.
What are odds ratios? How are they calculated and interpreted? - Odds ratios are ratios of 2 odds and
are calculated as follows:
OR = (odds of disease/exposure in the exposed/diseased group)/(odds of disease/exposure in the non-
exposed/non-diseased group)
or : OR = (ad)/(bc)
In cohort studies --> an OR >1 means that the odds of disease are greater in the exposed group than the
non-exposed group
, In case-control studies --> an OR >1 means that the odds of exposure are greater in the diseased group
than the non-diseased group
Under what circumstances do the RR and OR closely approximate each other? - The RR and OR closely
approximate each other when the outcome of interest is a rare disease.
What are incidence rate ratios? How are they calculated and interpreted? - The incidence rate ratio is a
ratio of incidence rates between 2 groups and is calculated as follows:
IRR = incidence rate of disease in exposed group/incidence rate of disease in a non-exposed group
or: IRR = (a1/t1)/(ao/to)
An IRR >1 means that incidence rate of disease in the exposed group is greater than the incidence rate in
the non-exposed group
What is risk/rate difference? How is it calculated and interpreted? - Risk/rate differences measure the
difference in risk or rate of the outcome in the exposed and non-exposed groups.
Risk difference = P(D+|E+) - P(D+|E-)
Rate difference = (rate in E+) - (rate in E-)
The RD>0 represents the excess risk/rate of the outcome in the exposed group.
What is the attributable proportion exposed? How is it calculated and interpreted? - The AP measures
the proportion of risk or rate of the outcome in the exposed group that is attributable to the exposure.
For risk data: AP = risk difference/P(D+/E+)
For rate data: AP = rate difference/(rate in E+)
The AP represents the % of the outcome in the exposed group that is caused by exposure.
Les avantages d'acheter des résumés chez Stuvia:
Qualité garantie par les avis des clients
Les clients de Stuvia ont évalués plus de 700 000 résumés. C'est comme ça que vous savez que vous achetez les meilleurs documents.
L’achat facile et rapide
Vous pouvez payer rapidement avec iDeal, carte de crédit ou Stuvia-crédit pour les résumés. Il n'y a pas d'adhésion nécessaire.
Focus sur l’essentiel
Vos camarades écrivent eux-mêmes les notes d’étude, c’est pourquoi les documents sont toujours fiables et à jour. Cela garantit que vous arrivez rapidement au coeur du matériel.
Foire aux questions
Qu'est-ce que j'obtiens en achetant ce document ?
Vous obtenez un PDF, disponible immédiatement après votre achat. Le document acheté est accessible à tout moment, n'importe où et indéfiniment via votre profil.
Garantie de remboursement : comment ça marche ?
Notre garantie de satisfaction garantit que vous trouverez toujours un document d'étude qui vous convient. Vous remplissez un formulaire et notre équipe du service client s'occupe du reste.
Auprès de qui est-ce que j'achète ce résumé ?
Stuvia est une place de marché. Alors, vous n'achetez donc pas ce document chez nous, mais auprès du vendeur VasilyKichigin. Stuvia facilite les paiements au vendeur.
Est-ce que j'aurai un abonnement?
Non, vous n'achetez ce résumé que pour $13.48. Vous n'êtes lié à rien après votre achat.
