What is a confidence interval?

a range of estimates for an unknown parameter

What does a 95% confidence level mean?

that the confidence interval should contain the true effect of intervention 95% of the time

What is standard error of the mean?

a measure of the spread expected for the mean

a.k.a how 'accurate' the calculated sample mean is from the true population mean

How is standard error of the mean calculated?

• SEM = SD / square root (n)
• where SD = standard deviation and n = sample size
• therefore the SEM gets smaller as the sample size (n) increases

How would you calculate a 95% confidence interval?

• lower limit = mean - (1.96 * SEM)
• upper limit = mean + (1.96 * SEM)