A comparison of sampling error and standard error

The impact of a diet and physical activity programme on body weight in overweight or obese people initiated through a national colorectal cancer screening programme was investigated. A multicentre randomised controlled trial was performed. The intervention consisted of a personalised, behaviourally focused weight loss programme, delivered over 12 months. The control treatment consisted of a weight loss booklet only. Participants were overweight or obese adults (aged 50-74 years) who had undergone colonoscopy after a positive faecal occult blood test result and had a diagnosis of adenoma confirmed by histopathological examination. In total, 329 participants were recruited and randomised to the intervention (n=163) or control (n=166).1

The primary outcome was weight change over 12 months. At follow-up, data were available on the primary outcome for 148 (91%) participants in the intervention group and 157 (95%) in the control group. At 12 months, mean weight loss was 3.50 kg (95% confidence interval 2.70 to 4.30; standard error 0.40) in the intervention group compared with 0.78 kg (0.19 to 1.38; 0.30) in the control group. The intervention group lost significantly more weight (mean difference 2.69 kg, 1.70 to 3.67; P<0.001). It was concluded that significant weight loss can be achieved by a diet and physical activity intervention initiated within a national colorectal cancer screening programme in older adults, offering considerable potential for reducing the risk of disease.

Which of the following statements, if any, are true?

• a) The sample estimates were …