- An interim analysis will be performed annually (i.e. after inclusion of 1/3 and 2/3 of the patients) to to allow early stop of the study (or accrual of patients in a specific treatment group) due to rejection of the null hypothesis. Using the O'Brien-Fleming method (O'Brien and Fleming 1979) results in respectively |3.471|, |2.454| and |2.004| as critical values for the Z-statistic at the three analysis moments. Otherwise stated, p-values are declared significant if <.00052, <0.0141 and <0.0451 at respectively the first interim analysis, the second interim analysis and at the final analysis.