Leprosy Mailing List – August 1^st, 2007

  

Ref.:     Numerators and denominators should come from the same source

From:   Post E., Wuerzburg, Germany

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Dear Salvatore,

 

I refer to your message dated LML July 31^st, 2007.  I don’t think that working with rates will change the issue, see the example below in which all factors were kept constant in 3 consecutive years, except that in year 2 only 5/6 countries reported and in year 3 only 4/6 countries reported.  It still results in non-comparable global rates.

 

This is logical of course, as both numerator and denominator change!  In the end one can only compare situations whereby numerators and denominators come from the same source.

 

Trends are therefore better to be followed for a set group of countries from which each and every year data are obtained.  If this is not possible, one must look at country levels, but also here we know that not all countries have their statistics complete at the moment of data gathering, and thus even country-level data over a few years must be analysed with caution.

 

Year 1:

country	population	Cases	rate/100,000
1	100.000.000	5.000	5,0
2	4.000.000	300	7,5
3	50.000.000	500	1,0
4	20.000.000	400	2,0
5	10.000.000	300	3,0
6	500.000.000	150.000	30,0
total	684.000.000	156.500	22,9
Year 2:
country	population	Cases	rate/100,000
1	100.000.000	5.000	5,0
2	4.000.000	300	7,5
3	50.000.000	500	1,0
4	20.000.000	400	2,0
5	10.000.000	300	3,0
total	184.000.000	6.500	3,5
Year 3:
country	population	Cases	rate/100,000
1	100.000.000	5.000	5,0
2	4.000.000	300	7,5
5	10.000.000	300	3,0
6	500.000.000	150.000	30,0
total	614.000.000	155.600	25,3

 

Best regards,

 

Erik Post

 

Erik Post, MD MSc, Medical Advisor

German Leprosy and Tuberculosis Relief Association

Mariannhillstr. 1-C, 97074 Wuerzburg, Germany

Tel:  +49 931 7948 113          Fax: +49 931 7948 160

Email: erik.post@dahw.de     Internet: www.dahw.de