Thread: measuring standard error

The story: healthy three year olds have a mean weight of 12.1515 and a standard deviation of 1.3448

I have a sample of children and I'm comparing it to the population of healthy babies.


the question im faced with is:

"How many standard errors (to the nearest hundredth) is the sample mean different from the expected mean for a healthy population (e.g. -4.34)"

sample 1 mean = 12.045 kg so the difference is |12.045-12.1515| and then that is divided by the standard error.

standard error is given by

(standard deviation)/sqrt(n) where n is the sample size.



So the question is which standard deviation do I use? the sample SD or the population SD?

my guess is that I should use the sample SD, but since we are comparing our sample to the population maybe measuring the distance in means using the population SD is best?

Hi kingsolomonsgrave!

If you have a choice, always compare against the population SD.
The sample SD is (usually) only a bad approximation of the population SD.

thanks!