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Biotech / Medical : XOMA. Bull or Bear? -- Ignore unavailable to you. Want to Upgrade?

To: Robert S. who wrote (8416)	1/22/1999 10:27:00 AM
From: aknahow	Respond to of 17367

Thanks Robert_S, always appreciate your help.

To: Robert S. who wrote (8416)	1/22/1999 12:44:00 PM
From: Cacaito	Read Replies (4) \| Respond to of 17367

Total deaths is total nonsense. If one has N 100, meaning 100 on each group: Case 1 - One expects 25% deaths in placebo group, and 10% in Bpi group, then 35 deaths is the total. The N 100 ( 200 patients ) is enough to show statistical significance. Case 2 - Now get 20% in placebo, and 15% in bpi, still one has 35 deaths for the same N 100 (200 patients), but the N is not enough to be statistically significant. A higher N, like 300 could show it (600 patients)and it will be important. Case 3 - Now get 18% placebo, 17% bpi, Still one have total deaths of 35, but to proof significance here one needs about N 15,000 (30,000 patients). One start with the mortality in %, continue with how much one expects it to go down in %, choose Power (usually 80 when mortality is the outcome to change) then use Chi Square analysis to get your N (number of subjects needed on each group). The total deaths are a byproduct of the calculations one start with, not the begining and not the aim. the aim is a moving complex target mortality difference between two groups of subjects. The comment about lack of ability to get enough patients to show Statistical significance due to the low incidence of the disease is not right (William himself post he was not sure. One needs just the time and the effective drug (xoma has plenty of time). There are suggestions that mortality has come down in this disorders, It has not in patients already shock all near shock. The UK interventions are due to a higher than expected number of patients, and recommedations for early antibiotics. In the Spain report (Barcelona area only)a very similar population to the UK and US and very good health care (not Third world type)the mortality was less in patients who have antibiotics prior to diagnosis , most of then had the antibiotics for other conditions, or for very early signs interpreted as other disorders, many of then had just simple oral antibiotics for sore throat and later developed the disease, nothing new here that is why there are protocols (Rifampin) for individuals exposed to meningococcemia patients, it works. If Xoma's trial is about shock type patients like in the pahse II, they already has very good numbers to show statistical significance. My view is that the company is going very conservative and I agree with extending the trial if they are not halted (DSMB has not). If Xoma is taking all type of patients (shock and non-shock) then they will need many, many more subjects, then again I agree. Another observation about UK data is that a lot of the "increase" is due most probably to the use of PCR (polymerase chain reaction) technique for diagnosis since 1996 (when the "increase" starte). The PCR technique allows to identify the bacteria with only one bacteria per 1,000,000 white cells (not the exact number, but get the idea of how it could look for a needle in a haystack and find it). And do not confuse the increase recruting from UK by xoma as the same as increase incidence of disease. The initial date line (12/98) was a guideline from the company not a leagal set. The 200 patients was an initial number, they do not know the blind data, but they do know the total deaths and some inference could be done, if they decided to extend trial then fine. Check PARS thread, the company itself provided to the public the total deaths in their phase II before unblinding, everybody made calculations, when data came out everybody found the unexpected, the numbers were very similar and even if they showed a 26% decrease in mortality the N was not enough to show statistical significant, that is why the stock is $1.5 and not $15. And they are waiting now for starting PIII.