Practical Manual - Malareo

This tells you how wide spread Malaria is within your population. Unlike the common cold which is
transitory in nature, Some strains of Malaria can recur within an infected individual and therefore once
infected the infected numbers can be considered cumulative.
Now you will calculate the prevalence for all Malaria case locations reported. You will do this by creating
a new field in your table and updating it using the field calculator
Make sure your malaria_case-Health_facility.shp file is in the legend. Open the attribute table and
toggle editing on. Within the Window the icon to “New column”
becomes active.
Add a field called “prevalence”, Make the data type decimal
Number (real), the width3 and the Precision 2 (this sets the with
of the column at 3 and allows for 1 decimal place. You can add a
comment To tell users what the column means (prevalence
figures for Malaria 1999 – 2008) Click on OK. You will find the
column at the end of the table
Now you will update this
column.
Open the Field calculator
using the field calculator icon. This opens the filed
calculator.
Within the field calculator you will have to
construct a mathematical formula using the
existing columns to calculate prevalence (This will
be the sum of all infections per year e.g.
SUMOF1999_ divided by the total population
multiplied by 100 to get a percentage)
You will be updating an existing field namely the
column (field) “Prevalence” that you just dreated
The formula to use is shown below and can be
constructed by double clicking on each field and
using the operators to add each one to the Expression.
((SUMOF1999_ + SUMOF2000_ + SUMOF2001_ + SUMOF2002_ + SUMOF2003_ +
SUMOF2004_ + SUMOF2005_ + SUMOF2006_ + SUMOF2007_ +
SUMOF2008_)/POP05)*100
Once complete Toggle editing off and Save changes and you will see a column
QGIS for Malaria Page 60