Suggest you start with the "simplest" approach: do a Chi-Square
test, where null hypothesis is: frequency is independent of time in
shift. I believe it will show the difference is statistically
significant.
If I were the manager, I would then ask for a breakdown by hour - was
the first part of the shift much more hazardous than the rest of the
first half?
Sort of puts the lie to the idea that tired workers near the end of a
shift are more dangerous to themselves than earlier....
Or is it possible that many workers leave the work site during the
shift, so that there are simply more people in the shop during the
first half of the shift?
Jay
On Oct 19, 2008, at 1:09:23 PM, Kaveh Asanati wrote:
> Dear allstat,
>
> Hope you all have had a nice weekend. I wonder if you could please
> advise me on the following question:
>
> In my study, I have found that of 169 occupational injuries
> occurred in a factory, 116 injury events occurred in the first half
> of the working shift and 53 in the second half of the shift.
>
> Although it is clear that the number of injury events is
> significantly higher in the first half of the shift, I am not clear
> how I could show the effect size; would you please advise? (i.e. if
> I need to go for odds ratio, ratio of proportions, relative risk or
> …).
>
> Thank you very much for your assistance in this matter.
>
> All the best,
> Kaveh
>
>
Jay Warner
Principal Scientist
Warner Consulting, Inc.
4444 North Green Bay Road
Racine, WI 53404-1216
USA
Ph: 262.634.9100
Fax: 262.681.1133
email: [log in to unmask]
web: www.a2q.com
The A2Q Method (tm) -- What do you want to improve today?
Jay Warner
Principal Scientist
Warner Consulting, Inc.
4444 North Green Bay Road
Racine, WI 53404-1216
USA
Ph: 262.634.9100
Fax: 262.681.1133
email: [log in to unmask]
web: www.a2q.com
The A2Q Method (tm) -- What do you want to improve today?
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