8 a and b. A randomization scheme balanced for female/male, as well as for surgery/non-surgery patients was performed by using random permuted blocks of 20 (10 females and 10 male) patients in order to reduce predictability. The permutation blocks were randomly chosen. Two sets of closed envelopes in numbered orders, one set for males and one for females, with either message "operate" or "do not operate" were delivered to the clinic by the statistician not involved in the treatment of the patients.