Skewed distributions IIBMJ 2010; 341 doi: https://doi.org/10.1136/bmj.c6448 (Published 17 November 2010) Cite this as: BMJ 2010;341:c6448
- Philip Sedgwick, senior lecturer in medical statistics
- 1Section of Medical and Healthcare Education, St George’s, University of London, Tooting, London, UK
Researchers investigated the effects of long term treatment with metformin on the risk of vitamin B12 deficiency in patients with type 2 diabetes receiving insulin treatment.1 A multicentre randomised placebo controlled trial was used. A total of 390 patients were randomly assigned to receive 850 mg metformin or 850 mg placebo three times a day.
Primary outcome measures included percentage change in the serum concentration of homocysteine from baseline at 4, 17, 30, 43, and 52 month follow-up. At baseline, the metformin group (n=196) had a mean homocysteine concentration of 14.4 μmol/l (standard deviation 9.7 μmol/l), compared with a mean concentration of 14.6 μmol/l (standard deviation 10.3 μmol/l) for the placebo group (n=194).
Which of the following statements, if any, are true for the metformin group at baseline?
a) Approximately 68% or more of the homocysteine measurements were no further than one standard deviation away from the sample mean …