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In a medical paper 150 patients were characterised as 'Age 26 years ± 5 years (mean ± standard deviation)'. If the ages were normally distributed, this means that:

1. It is 95% certain that the true mean lies in the interval 16-36 years

2. Most of the patients were aged 26 yrs; the remainder were aged 21-31 yrs

3. Approximately 95% of the patients were aged between 16 and 36 years

A pharmacokinetic investigation, including 216 volunteers, revealed that the plasma concentration one hour after oral administration of 10mg of the drug was 188ng/ml ± 10ng/ml (mean ± standard error). This implies that:

1. 95% of the volunteers had plasma concentrations between 168 and 208ng/ml

2. The interval 168 to 208 ng/ml is the normal range of the plasma concentration 1 hour after oral administration.

3. We are 95% confident that the true mean lies somewhere within 168-208 ng/ml

The standard error of the mean of a sample:

1. Can be calculated using the standard deviation of the population and the size of the sample

2. Measures how far the sample mean is likely to be from the population mean

3. Is greater than the standard deviation of the observations