Which PROC FREQ 95% CI can handle zero counts, if any?

[mariko5797]

I want to find the relative risk and risk difference and their corresponding 95% CIs to compare adverse events in a treatment group compared to a placebo group. 

What 95% CI can handle zero counts using PROC FREQ (or a different procedure)? I was going to use Wald and Agresti-Caffo, respectively, but it looks like Wald can't handle zero counts and since we have a small sample size (n<10), perhaps that's not the best option in general...

[PaigeMiller]

What does "handle" mean in this context? It seems to me that PROC FREQ handles zero counts properly, by my definition of "handle".

[mariko5797]

For example, SAS documentation states if any of the cells are zero, then Wald 95% CI cannot be computed.

[PaigeMiller]

Yes, in that case, SAS "handles" it properly, as far as I know.

[mariko5797]

I see what you mean. Let me re-phrase then, are there any methods that will give me 95% CI if there is a zero in one of the cells? Are would they all be non-calculable?

[SAS_Rob]

Unfortunately, PROC FREQ doesn’t provide RISKDIFF analysis for two-way tables when there is a zero-frequency column(both treatment arms have no positive responses). In the meantime the work-around to assign very small weights to the zero-frequency cells in your two-way table is the only option. When you use this work-around, the following confidence limit types are available for the risk difference: Agresti-Caffo, Hauck-Anderson, Miettinen-Nurminen (score), and Newcombe. Of course the traditional/Wald confidence limits are also available, but equal (0,0) in the case of a zero-frequency column where the estimate of the risk difference is 0.   

[mariko5797]

What about for relative risk?

[SAS_Rob]

This approach would also work for the relative risk with all of the CL= options other than EXACT.

[data_null__]

I don't know if it will work or be statistically correct, but you could try setting the zero cell to a very small WEIGHT 1e-11 and see what happens.

Also, showing your work.