Date:         Mon, 21 Apr 2008 00:10:29 +1000
Reply-To:     "Cooper, Tim (Australia)" <tim_cooper@merck.com>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         "Cooper, Tim (Australia)" <tim_cooper@merck.com>
Subject:      Confidence Interval for Lost Time accidents?
Content-Type: text/plain; charset="us-ascii"

Hi,

If a Lost Time Accident rate was 6 incidents last year and the target is
4 this year, is this a realistic target, i.e. it possible to show that
these rates are not significantly different?

Common sense says that if you have over a thousand employees and
typically only have 5 to 7 Lost Time Accidents a year, then this is so
close to 4 that it is probably not significantly different.  But how do
I calculate this?  

These rates are not far from zero anyway and there'll always be some one
who makes a mistake, so decreasing the target below some level is
probably not workable.

If I apply a binomial approach, what do I set N as?  Any employee could
have more than one Lost Time Accident, so the N can't simply be the
number of employees.  The Binomial Test's required assumption of
independence may not apply as the same process or even same person could
be responsible.

Really appreciate any help on this as I don't recall this problem on my
stats courses!


Regards, 

Tim Cooper


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