[EpiData-list] EpiData Analysis - Definition of histogram

epidata-list at lists.umanitoba.ca epidata-list at lists.umanitoba.ca
Sat May 12 15:30:45 CDT 2007

I agree. However, the question of x-axis increment is not fully defined. 
There are two aspects to this. The usual option /xinc= will only affect 
the labelling on the chart, as with other graphs. However, the interval 
used to define boxes is something that should also be an option with 
histogram. This is particularly important for epicurves. This means that 
we can avoid awkward recoding of variables (especially tricky with 
dates) to have an epicurve that groups cases by 4-hour intervals, for 
example, and also labels the x-axis every 12 hours:

epicurve onsettime case /xinc=12 /interval=4

The same would be true of a histogram by age, where we wanted age 
grouped by 5 years. I would prefer

       his age /interval=5 /xinc=10


       define age5 ##
       age5 = age div 5
       his age5 /interval=5

Right now, his and epicurve are constrained to intervals of 1, which 
means that labelling is not always correct.

Jamie Hockin
Public Health Agency of Canada

Jens wrote:
> After constructive comments from Egil Arnesen in Tromsø, Norway and 
> searching in various textbooks I have decided that for v2 the 
> following two definitions will be implemented:
> histogram:
> A graph, where there is one bar for each value present in the data. 
> The height of the bar corresponds to the count of records in the data. 
> (possibly later the percentage of data). Each bar starts at the 
> x-value which was in the data (e.g. age 45 is shown from 45-46.) And 
> the width of one bar is the same as the unit of the x variable.
> The X-axis is numerical and can be scaled with minimum, maximum and 
> increase.E.g. from 25 to 100 with tickmarks by 5 (25 30 35 ......95 100)
> Bar:
> A graph, where there is one bar for each value represented in the 
> data. The X-axis is categorical and the bar is centered around the 
> tick mark, which would show the value label (or the value) given by 
> the x value.
> If anyone has comments to this please send to this list.
> The principle of the histogram will be implemented also for EpiCurve 
> (but has not been done yet). The mentioned implementation of bar and 
> histogram should work from build 112 uploaded shortly before this 
> mail. (Minor problem with the build 112 uploaded yesterday).

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