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

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epidata-list@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/cbrchttps://webmail.accv.org.au/exchweb/bin/redir.asp?URL=http://www.cancervic.org.au/cbrc

On 2/26/07, epidata-list@lists.umanitoba.ca epidata-list@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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