Researchers investigated the efficacy of a probiotic drink containing Lactobacillus for the prevention of antibiotic associated diarrhoea in patients over 50 years. A randomized double blind placebo controlled trial study design was used. The intervention consisted of consumption of a probiotic drink twice a day during a course of antibiotics and for one week after the course finished. The placebo was a long life sterile milkshake. The primary outcome was occurrence of antibiotic associated diarrhoea.
Participants were recruited from three London hospitals. A total of 1760 patients were assessed for eligibility, 1625 of whom were not recruited because they did not meet the inclusion criteria (n=1263), refused to participate (n=148), or could not be included for practical reasons (n=214). The remaining 135 patients were recruited to the trial and randomised to intervention (n=69) or placebo (n=66). In total, 12 patients receiving the intervention and 10 in the placebo group did not complete their treatment protocol because they were lost to follow-up, withdrew consent, or died during the study period. The trial was analysed using a per protocol analysis. The researchers reported that consumption of the probiotic drink reduced the incidence of antibiotic associated diarrhoea.
Which of the following statements, if any, are true?
a) The random allocation of patients promoted external validity
b) The random allocation of patients promoted internal validity
c) The per protocol analysis promoted internal validity