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Statistics LibreTexts

20.20: Weight and Sleep Apnea

Skills to Develop

  • Excess Body Weight and Sleep Apnea  

Research conducted by

Kari Johansson, Erik Hemmingsson, Richard Harlid, Ylva Trolle Lagerros, Fredrik Granath, Stephan Rössner, and Martin Neovius 

Statistical article authored by

Philip Sedgwick

Case study prepared by

Robert F. Houser and Georgette Baghdady


In his statistical article, “Standard deviation versus standard error,” UK researcher Philip Sedgwick presents us with an interesting discussion of the proper use of standard deviation (SD) and standard error of the mean (SEM).  He uses an example of a weight loss study of \(63\) obese men suffering from obstructive sleep apnea who were being treated with continuous positive airway pressure (CPAP).  The weight loss program lasted one year.  Outcome measures included change in body weight measured in kilograms (kg).

More than \(60\%\) of people experiencing obstructive sleep apnea are obese.  CPAP therapy is the most common treatment.  It uses a machine and mask to prevent the airway from collapsing, thus enabling a person to breathe more easily during sleep.  Weight loss is an effective treatment for sleep apnea. 

Questions to Answer

What is the proper use of the SD?  What is the proper use of the SEM?

Design Issues 

None for the Sedgwick article. 

Descriptions of Variables

Table \(\PageIndex{1}\): Description of Variables

Variable Description
Weight Body weight at baseline in kg
Weight change Change in body weight at one year from baseline in kg


  • Sedgwick, P. (2011). Standard deviation versus standard error. BMJ, 343, d8010.
  • Johansson, K., Hemmingsson, E., Harlid, R., Lagerros, Y. T., Granath, F., Rössner, S., Neovius, M. (2011). Longer term effects of very low energy diet on obstructive sleep apnoea in cohort derived from randomised controlled trial: prospective observational follow-up study. BMJ, 342, d3017.


  • Online Statistics Education: A Multimedia Course of Study ( Project Leader: David M. Lane, Rice University.