# why i can not post my question?

#### Menekse

##### New Member
I tried 3 times until now.
when odds ratio is not possible due to 0 outcome risk estimate can be calculated for the control group ( SPSS, descriptive statistics, crosstabs, risk). So how I should understand the risk value form the the tables?
thanks

#### Dason

Did you try posting with this user account or did you make a different account to post this?

#### hlsmith

##### Less is more. Stay pure. Stay poor.
Can you provide your contingency table data. Is it possible you have not sample enough people?

A possible fix is to add a nominal amount to all of the cells, typically 0.5 (referred to as acontinuity correction). You would just want to disclose the use of this approach when reporting the results.

#### Menekse

##### New Member
I sent it on this page. Used the visitor message, then something else. But as I see now, I am successful with it. Thanks

#### Menekse

##### New Member
Sorry the second message would go to another member

#### Menekse

##### New Member
Sorry. as I see I am not successful with sending my first reply.
Here is it.
Yeah I do not have enough people. But the problem with the data is the outcome is 0 for some outcomes under the same risk factor. So SPSS did not calculate odds ratio for these outcomes and jumped to Risk Estimate which is even harder to understand for me.
Now do you mean I must add 0.5 to all cells even to those which caused 0 outcome on the crosstabs?
Many thanks

#### hlsmith

##### Less is more. Stay pure. Stay poor.
Normal relative risk = a \ (a+b) over c \ (c + d), so a zero results in an undefined. If you add 0.5 to all values you can get a result

#### Menekse

##### New Member
Thank you very much! I understand what to do. I will add this value just to calculate the risk and report it in the statistical analysis section only for the odds ratio calculation. I did all the previous analysis before fixing the values used to calculate the odds ratio. As a statistical approach, is that fine?

#### Menekse

##### New Member
Hi, Although I added 0.5 to all the cells the result or risk estimate did not changed. I got the same results: 0 still exist on the crosstabs and odds ratio was not calculated for the risk. Only risk estimate for 0,5= no outcome was calculated...
There is no attachment button here to send the analysis as I see...
Thank you.

#### hlsmith

##### Less is more. Stay pure. Stay poor.
Are you controlling for other variables or is this a straight 2x2 table scenario? If you are not controlling for variables, you can just calculate it by hand.

Also, risk and odds are not the same thing and should not be used interchangeably.

#### Menekse

##### New Member
I calculated correlation seperately between 6 risk factors and 5 outcomes. Then I needed to add odds ratio.
Yes it is a 2×2 table.
I can see the risk estimate include odds ratio. but it is different from it....
Thanks

#### hlsmith

##### Less is more. Stay pure. Stay poor.
Risk = a / a + b

Odds = a / b

They are not the same. If the exposure of interest is rare, then the odds can approximate the risk. Risk is usually used if you have temporality in data (e.g., collect exposure then document subsequent outcome) and odds if data collect retrospectively or via cross-section without knowledge of temporality. Odds and odds ratios get used more frequently since they can be easily generated from logistic regression.

#### Menekse

##### New Member
Thank you very much.

Last edited:

#### Abubakar Mshelia Saidu

##### New Member
Dear Sir/Ma
Group C is a control group. No surgeries to the group but sampled as the other 3 groups that had different techniques of a rumenotomy procedure. Each group had 3 males and 3 females as sub group. Sampling were before surgery as PRE,then postsurgeries as 0hr, 5hrs, 24hrs,48hrs, 72hrs, weeks 1,2 and 3. How do I compare the groups. I'm using graphpad prism 5.
Assays were for Cytokines.

Thank you.