We now introduce a more complex 'real life' clinical trial. Measurements from this trial will be used to provide data for several examples in future chapters. Although it is by no means the only example we will be presenting, by the repeated use of this trial we hope that the reader will identify more readily with the analyses.
The trial was a randomised double blind comparison of three treatments for hypertension and has been reported by Hall etal. (1991). One treatment was a new drug (A) and the other two (B and C) were standard drugs for controlling hypertension (A = Carvedilol, B = Nifedipine, C = Atenolol). Twenty-nine centres participated in the trial and patients were randomised in order of entry. Two pre-treatment and four post-treatment visits were made as follows:
• Visit 1 (week 0): Measurements were made to determine whether patients met the eligibility criteria for the trial. Patients who did so received a placebo treatment for one week, after which they returned for a second visit.
• Visit 2 (week 1): Measurements were repeated and patients who still satisfied the eligibility criteria were entered into the study and randomised to receive one of the three treatments.
• Visits 3-6 (weeks 3, 5, 7, 9): Measurements were repeated at four post-treatment visits, which occurred at two-weekly intervals.
• Three hundred and eleven patients were assessed for entry into the study. Of these, 288 patients were suitable and were randomised to receive one of the three treatments. Thirty patients dropped out of the study prior to Visit 6.
• Measurements on cardiac function, laboratory values and adverse events were recorded at each visit. Diastolic blood pressure (DBP) was the primary endpoint and we will consider its analysis here.
• The frequencies of patients attending at least one post-treatment visit at each of the 29 centres are shown in Table 1.1.
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