[EpiData-list] Entering time and date for outbreaks

epidata-list at lists.umanitoba.ca epidata-list at lists.umanitoba.ca
Mon Feb 26 16:25:01 CST 2007


Hi Charity

Thanks very much for your formula. Its sounds really good. I had a go
at putting it in a check file. Following through your example below
'Diatime' is my 'vtime2' and 'diadate' is my vdate2. I thought I would
start off slowly by seeing if I coudl calculate Vhours2. I created a new
field called Vhours2 in my rec file and then I put the following code
into the check file. 
 

DIATIME
  AFTER ENTRY
    LET VHOURS2=INT(DIATIME)+(FRAC(DIATIME)/0.6)+(DIADATE*24)
  END
END

Epi accepted the code but nothing appears in the vhours2 field when I
enter information in the diadate and diatime fields. Can you see what I
am doing wrong?


thanks

Christine Roseveare
Analyst
Regional Public Health
570 9194
027 495 9671




>>> <epidata-list at lists.umanitoba.ca> 26/02/2007 7:24 p.m. >>>
Hello Chrsitine,

I prefer to enter times as a decimal field, i.e. ##.##. I can then put
checks in place to make sure the minutes are in correct time format
e.g. IF
Frac(vtime) > 0.59 THEN ....

Based on this decimal 24 hour time format, I have a formula which you
can
use to calculate the difference in hours between two time and date
combinations.

Assume that your first time and date are vtime1 and vdate1, and your
second
time and date are vtime2 and vdate2:

First calculate the number of hours (since 31st December 1899) for both
time
and date combinations (store them as vhours1 and vhours2) using the
following formulae:

    vhours2=Int(vtime2) + (Frac(vtime2)/0.6) + (vdate2*24)
    vhours1=Int(vtime1) + (Frac(vtime1)/0.6) + (vdate1*24)

And then you can just calculate the time difference /incubation period
into
a different variable!


    timediff=vhours2-vhours1

You could also have done something similar and perhaps simpler using
EpiData's Time2Num function which will convert a decimal time into a
number
between 0 and 1 representing a fraction of a day - I just prefer to
work
with hours.

To explain the hours calculation formula for you (only need to read
below if
you care how the formula works):
Int(vtime) takes the integer part of the time, and Frac(vtime) takes
the
fractional part of the time. These are separated so Frac(vtime) alone
can be
converted from minutes into fraction of an hour (e.g. from 0.30 to
0.50).
The date integer (representing the number of days since 31 Dec 1899) is
then
multiplied by 24 to get the number of hours since 31 Dec 1899. This
1899 date is relevant only because it is how EpiData stores the date as
an
integer - we do not have to worry about this because we only care about
the
difference between the two dates.

Hope this helps!

Charity

Charity Jenkins
 Data Processing Officer
Centre for Behavioural Research in Cancer
The Cancer Council Victoria
http://www.cancervic.org.au/cbrc<https://webmail.accv.org.au/exchweb/bin/redir.asp?URL=http://www.cancervic.org.au/cbrc>


On 2/26/07, epidata-list at lists.umanitoba.ca
<epidata-list at lists.umanitoba.ca>
wrote:
>
> Hello everyone
>
> I am after advice about the best way to record time and date
> information when collecting information about food poisoning
outbreaks,
> given epidata does not have a time/date field. We want this
information
> to estimate incubation periods, in order to get clues about the
likely
> illness.
>
> Incubation
> Incubation = time from when someone is exposed to the time they
become
> unwell.
> For example someone may eat a buffet meal at 7pm on 21 February and
> become unwell at 1am on 22 February = incubation of 6 hours.
>
> Current method
> At the moment we:
> a) enter information in two fields. OnsetDay is recorded in a date
> field, and onsettime in a numeric field (####)
> b) list the two fields (using epi info) to view the information
> c) calculate incubation manually.
>
> Is there a better/easier way to do this? Also what is the
recommended
> way for entering 24 clock time - should 7.30pm be 1930 or 19.30
>
> thanks very much
>
> Christine
>
>
>
> Christine Roseveare
> Analyst
> Regional Public Health
> 570 9194
> 027 495 9671
>
>
>
>
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Hutt Valley DHB. 
Thank you.
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