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→Calculating measures of effect and impact
[[Category:Veterinary Epidemiology - Statistical Methods|D]]
[[Category:Veterinary Epidemiology - Statistical Methods|D]]
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==Calculating measures of effect and impact==
Measures of effect and impact can be calculated using the same contingency table used to calculated measures of strength of association: <br />
{| class="wikitable"
{| class="wikitable"
|-
|-
| Diseased || a<sub>1</sub> || a<sub>0</sub> || m<sub>1</sub>
| Diseased || a<sub>1</sub> || a<sub>0</sub> || m<sub>1</sub>
|-
|-
| Non-diseased || b<sub>1</sub> || b<sub>0</sub> || m<sub>0</sub>
| Non-diseased || b<sub
== Heading text ==
>1</sub> || b<sub>0</sub> || m<sub>0</sub>
|-
|-
| Total || n<sub>1</sub> || n<sub>0</sub> || n
| Total || n<sub>1</sub> || n<sub>0</sub> || n
[[File:AF.jpg]]
[[File:AF.jpg]]
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===Population attributable risk (PAR)===
The '''population attributable risk''' is analogous to the risk difference in that it gives a difference in the risk between two groups; however PAR is an estimate of the amount of disease in the total '''population''' attributed to the risk factor. It is calculated as the overall risk in the population minus the risk in the unexposed group or by multiplying the risk difference by risk of disease in the population. PAR can only be estimated from studies where the groups selected are representative of the target population.</big><br />
The '''population attributable risk''' is analogous to the risk difference in that it gives a difference in the risk between two groups; however PAR is an estimate of the amount of disease in the total '''population''' attributed to the risk factor. It is calculated as the overall risk in the population minus the risk in the unexposed group or by multiplying the risk difference by risk of disease in the population. PAR can only be estimated from studies where the groups selected are representative of the target population.</sup><br />
[[File:PAR.jpg]]
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===Population attributable fraction (PAF)===
The population attributable fraction is the proportion of all cases in the population that could have been prevented by removal of exposure. It is related to the AF above and is calculated by dividing the PAR by the prevalence of disease in the study population.</big><br />
[[File:PAF.jpg]]
[[File:PAF.jpg]]