The role of ENSO in understanding changes in Colombia's annual malaria burden by region, 1960–2006

Malaria Journal

Table 4 Colombia's malaria models: predictand and predictor variable definitions

Predictand Variable	Description
M_T	Colombia's Total Malaria Cases
M_R1	Colombia's Total Malaria Cases in West (Pacific) Region
M_R2	Colombia's Total Malaria Cases in North (Atlantic) Region
M_R3	Colombia's Total Malaria Cases in Midwest (Andean) Region
M_R4	Colombia's Total Malaria Cases in Southeast (Amazon) Region
M_R5	Colombia's Total Malaria Cases in Northeast (Orinoco) Region
Predictor Variable	Description
ENSO_Avg	Yearly index based on average of the 12 monthly data for each year (°C)
ENSO_Dom	Yearly index based on average of only those consecutive months having the dominant ENSO state (La Niña, neutral, or El Niño) (°C)
Trend1	Time reference variable t = 1, 2,..., 47 associated with 1960–2006 period
Trend2	Time reference variable t = 1, 2, 3...8 associated with 1999 – 2006 period; 0 otherwise (1960–1998)
Vextre♣	Dummy variable: takes value of 1 in 1999; 0 otherwise

^♣ This dummy variable is associated with the significant drop of malaria cases in 1999. It can be attributed to a change in the registration process of the infectious diseases surveillance system during the embedding period. The observation in 1999 has a high high leverage in any regression model, and thus it is treated as an outlier to diminish its impact on the estimation process.
The predictand (malaria case numbers) are for Colombia as a whole, and for each of the 5 regions defined in Table 3 and Figure 3. The predictors include two indices of the ENSO state, two trends, and the vextre for special treatment for the year 1999.

ISSN: 1475-2875