Exercise: Confidence interval in the talking time study

In the study of Langewitz et al. (2002) of the length of time for which patients spoke when explaining their problem to a doctor, The authors reported the following:

"Of the 330 patients who provided sociodemographic data, . . . mean age was 42.9 years (SD 18.2 (95% confidence interval 17 to 84) years)."

(Note that mean ± 1.96 standard deviations = 7.2 to 78.6 years, mean ± 1.96 standard errors = 40.9 to 44.9 years.)


What is wrong with this confidence interval?

Check suggested answer.


Langewitz W, Denz M, Keller A, Kiss A, Rüttimann A, Wössmer B. (2002) Spontaneous talking time at start of consultation in outpatient clinic: cohort study. British Medical Journal 325, 682-683.

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Last updated: 19 January, 2009.

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