First of all we need to construct 2×2 contingency unmatched table.
It is as below
Cases | controls | Total | |
---|---|---|---|
Exposed to pond A | 194+46=240(a) | 194+6=200(b) | 440 |
Unexposed | 6+29=35(c) | 29+46=75(d) | 110 |
Total | 275 | 275 | 550 |
Unmatched OR formula = ad/bc
=240×75/200×35
=18000/7000
=2.57142857
Rounding into 2 decimal place= 2.57
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