Confidence interval and standard error of the mean

Question 1

What is a confidence interval?

Answer 1

A range of values for a variable of interest constructed so that this range has a specified probability of including the true value of the variable.

The specified probability is called the confidence level, and the end points of the confidence interval are called the confidence limits.

in simpler terms: a range of values within which the true effect of intervention is likely to lie

Question 2

What is the likelihood of the true effect lying within the confidence interval determined by?

Answer 2

The confidence level.

A confidence interval at the 95% confidence level means that the confidence interval should contain the true effect of intervention 95% of the time.

Question 3

What is the standard error of the mean?

Answer 3

A measure of the spread expected for the mean of observations i.e. how ‘accurate’ the calculated sample mean is from the true population mean.

Question 4

Calculation for the standard error of the mean?

Answer 4

SEM = SD / square root (n)

where SD = standard deviation
n = sample size

Question 5

Impact on SEM as the sample size increases?

Answer 5

SEM gets smaller

Question 6

Formula for the lower & upper limit of a 95% confidence interval?

Answer 6

Lower limit = mean - (1.96 * SEM)

Upper limit = mean + (1.96 * SEM)