help w/ what size sample to be 95% confident (sick days)

micmom3

New member
Joined
Mar 31, 2008
Messages
2
an insurance co. is trying to to estimate the number of sick days that workers take per year. a pervious study indicated that the standard deviation was 2.8days. how large of a sample must be selected if the company want to be 95% confident that the true mean differs from the sample mean by no more than 1 day

Thanks
 

Subhotosh Khan

Super Moderator
Staff member
Joined
Jun 18, 2007
Messages
18,149
Re: Please help

micmom3 said:
an insurance co. is trying to to estimate the number of sick days that workers take per year. a pervious study indicated that the standard deviation was 2.8days. how large of a sample must be selected if the company want to be 95% confident that the true mean differs from the sample mean by no more than 1 day
What are the z-values of the difference?
 

micmom3

New member
Joined
Mar 31, 2008
Messages
2
Re: Please help

explain
 

stapel

Super Moderator
Staff member
Joined
Feb 4, 2004
Messages
15,943
micmom3 said:
Are you saying that you need lessons on z-scores, etc?

Please be specific. Thank you! :D

Eliz.
 

royhaas

Full Member
Joined
Dec 14, 2005
Messages
832
micmom3 said:
an insurance co. is trying to to estimate the number of sick days that workers take per year. a pervious study indicated that the standard deviation was 2.8days. how large of a sample must be selected if the company want to be 95% confident that the true mean differs from the sample mean by no more than 1 day

Thanks
There is a simple formula for this kind of sample size problem. It should be in your textbook, possibly in the chapter that talks about confidence intervals for a normal mean with known standard deviation.
 
Top