Bosmana fem at 21:27, 22 March 2023

2023-03-22T21:27:36Z

← Older revision		Revision as of 21:27, 22 March 2023
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			[[Category:Effect Modification and Confounding]]

Bosmana fem: Created page with "=Explained= So far we have only considered that persons could be either exposed or not, but exposure can frequently be quantified and a gradient established. Examples may incl..."

2022-12-21T20:10:53Z

Created page with "=Explained= So far we have only considered that persons could be either exposed or not, but exposure can frequently be quantified and a gradient established. Examples may incl..."

New page

=Explained=
So far we have only considered that persons could be either exposed or not, but exposure can frequently be quantified and a gradient established. Examples may include the number of glasses (or volume) of water consumed per day, the number of pizza slices eaten, or the degree of completion of a vaccination course etc. The risk of illness can then be calculated according to amount drunk, eaten or completed.
{| class="wikitable"
! Amount drunk !! Exposed !! Cases !! Risk (%) !! RR
|-
| None || 100 || 5 || 5 || ref
|-
| 1 glass || 100 || 11 || 11 || 2.2
|-
| 2 glasses || 100 || 16 || 16 || 3.2
|-
| 3 glasses || 100 || 22 || 22 || 4.4
|-
| ≥4 glasses || 100 || 28 || 28 || 5.7
|-
| || 500 || 82 || 82 || c
|}

The Χ2 test for trend across these strata = 23.24, p≤0.001 - indicating that there is a trend across the exposure strata.

If instead a case control study had been conducted (note the similarity between the OR and the RR above):
{| class="wikitable"
! Amount drunk !! Exposed !! Cases !! OR
|-
| None || 5 || 30 || ref
|-
| 1 glass || 11 || 30 || 2.2
|-
| 2 glasses || 16 || 30 || 3.2
|-
| 3 glasses || 22 || 30 || 4.4
|-
| ≥4 glasses || 28 || 30 || 5.6
|-
| || 82 || 150
|}

For which the Χ2 test for trend = 12.77, p≤0.001

In the above examples, the risk of disease occurring increases with the amount of water consumed (i.e. with the dose of water). This is frequently called a dose response or a dose effect relationship.

To compute the risk ratio or the odds ratio the same reference level of exposure is used. Here the non exposed group is used as a reference. Alternatively the group with the lowest incidence could be used.

Dose response is particularly interesting when in an outbreak (often in water borne or a food borne outbreak) everybody is exposed to the same factor but the level of exposure differs among individuals. Choosing the lowest category of exposure as a reference still allows identification of a food item or a beverage as the vehicle for the outbreak. To test that the trend observed in risk or odds ratio differs from no trend, we can use a chi square for trend <ref>J.J.Schlesselman. Case-control studies: design, conduct, analysis. New York: Oxford University Press; 1982.</ref>, <ref>B.R.Kirkwood, J.A.C.Sterne. Medical Statistics. Second ed. Massachusetts: Blackwell Science Ltd; 2003.</ref>, <ref>K.J.Rothman, S.Greenland, T.L.Lash. Modern Epidemiology. Third ed. Philadelphia, USA: Lipincott Williams and Wilkins; 2008.</ref>. Dose response is also an important criterion to consider when providing evidence for causality proposed by Bradford Hill <ref>A.Bradford Hill. The Environment and Disease: Association or Causation? Proceedings of the Royal Society of Medicine 1965;58:295-300.</ref>.

=References=
<references/>

Dose Effect - Revision history

Bosmana fem at 21:27, 22 March 2023

Bosmana fem: Created page with "=Explained= So far we have only considered that persons could be either exposed or not, but exposure can frequently be quantified and a gradient established. Examples may incl..."