Screening for abdominal aortic aneurysm in men over 65 years of age has been recommended on the basis of several randomised controlled trials and meta-analyses. 1 2 These studies have shown that a single screening examination using ultrasound with follow-up intervention as appropriate can reduce aneurysm related mortality, with benefits extending to at least 10 years.
That meta-analysis and another study 25 concluded that on the basis of evidence from randomised controlled trials aspirin should not be given to all people with diabetes for primary prophylaxis of cardiovascular events but only to specific subgroups.
Individual-level correlation is usually first explored in observation cohort studies, as was the case in blood pressure, and is often the basis for subsequent evaluation in randomised controlled trials.
On the basis of results of previous randomised controlled trials (Moertel et al, 1969, 1981; Gastrointestinal Tumor Study Group, 1988), the combination of 5-FU therapy and radiotherapy has become a frequently employed treatment for locally advanced PC (Willett et al, 2005; Yip et al, 2006).
The new optimism has stemmed from the fact pirfenidone, licensed in Europe in 2011 on the basis of evidence from 4 randomised controlled trials (RCTs) [ 4- 6], has been shown in a recent multicentre RCT to slow the rate of progression of IPF [ 7].
The results of this study, along with other work in this research programme, will form the basis for the development and piloting of randomised controlled trials of primary care management of osteoarthritis symptoms in primary care.
Randomised controlled trials provide the appropriate basis for nutrition recommendations, but for demonstrating long-term effects there are problematic issues.
22 23 Twice as many of the randomised controlled trials that included qualitative work also had a clearly specified theoretical basis (40%) compared with randomised controlled trials without any qualitative work (20%).
