# Calculating Odds Ratios

#### shroomz

##### New Member
Would someone be able to help me figure out how to calculate the remaining odd's ratios in the table below? I am not able to reproduce the odd's ratios that have already been calculated either...really stuck!

#### hlsmith

##### Less is more. Stay pure. Stay poor.
OK, I am gonna make you work a little here and not spoon feed you.

So question #1, how can you get an OR of 1.0? How is that possible? Once you figure that out, you should be good to go.

Speak up, if you can't figure it out after a little effort!

#### shroomz

##### New Member
Thanks!! Ok so this is the 2x2 table I created to calculate the OR:

Could you give me a hint as to where I'm going wrong?

#### hlsmith

##### Less is more. Stay pure. Stay poor.
How do you get a ratio of 1, do the math!

Same number on top and bottom!
8/34 / 8/34

If you cant figure it out after this I'll tell you how to do it. Hint: Exclusive breastfeeding is always the reference group! Thus the denominator is always 8/34!

#### shroomz

##### New Member
Ah, okay so if exclusive breastfeeding is the reference group to which all the other groups (exposures) are compared, the missing ORs would be 3.9 (i.e. odds of case associated with mixed feeding is approx. 4 times higher than exclusive breastfeeding) and 14.45. Thanks a bunch for your help, kind internet stranger!!

#### hlsmith

##### Less is more. Stay pure. Stay poor.
No problem. I remember having to do these for school. The reference group was the tricky part. Another tricky one you may come across if continuing in th is area are additive and multiplicative effects.

feel free to post more questions in the future and welcome to the forum!