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Table 1 Results of uni-variate analysis from Stage 1. Odds Ratios (AIC in parentheses) from univariate logistic regression analysis of 50 different environmental variables from 7 themes, against malaria prevalence. P-values were non-significant (n.s.), <0.05(*), <0.01(**) or <0.0005 (***), n = 122. The equation was logit(prevalence) = coefficient × co-variate + constant. NDVI = normalized difference vegetation index.

From: Developing a spatial-statistical model and map of historical malaria prevalence in Botswana using a staged variable selection procedure

  Environmental data theme
Variable Rain-fall (mm) Temperature (°C) Vapor pressure (hPa) NDVI, 8 km resolution § NDVI, 1 km resolution § Other
Annual mean (total for rainfall) 1.0085 (27.6)** 4.22 (13.6)*** 1.094 (12.8)*** 1.091 (28.9)* 1.07 (31.3) n.s.  
Annual maximum (highest monthly value) 1.045 (20.8)*** 3.034 (23.3)*** 1.067 (11.7)*** 1.090 (25.7)*** 10.4 (32.2) n.s.  
Annual minimum (lowest monthly value)   3.29 (13.9)*** 1.11 (17.1)*** 1.1048 (29.8)* 1.06 (32.7) n.s.  
Annual range (highest minus lowest month)   0.52 (27.1)** 1.12 (15.8)*** 1.14 (30.8)* 1.03 (32.7) n.s.  
Standard deviation (Appendix) 1.03 (21.9)*** 0.54 (25.0)*** 0.54 (14.7)** 1.073 (26.6)*** 1.03 (32.8) n.s.  
Proportional standard deviation (Appendix)‡ 61.8 (13.0)*** -214 (17.3)*** 0.004 (33.4) n.s. 0.1 (26.8)*** 43.3 (32.9) n.s.  
Summer mean (total for rainfall) Dec–Mar 1.012 (22.9)*** 2.59 (27.1)*** 1.065 (11.6)*** 1.078 (28.9)*   
Winter mean (total for rainfall) Apr–Oct 0.88 (14.8)*** 3.22 (12.0)*** 1.11 (16.0)*** 1.097 (28.6)**   
Concentration (see Appendix) 1.39 (13.3)***      
Number of months >80 mm (>60 & >40 mm n.s.) 1.81 (26.6)**      
Number of months >16°C   2.72 (18.9)***     
Number of months >165 (other cut-offs were n.s.)     1.13 (31.5) n.s.   
Total in months with more than 80 mm 1.0059 (24.0)***      
Total degree months above 16°C   1.050 (15.7)***     
Effective temperature (Appendix)   21.8 (12.6)***     
Mean daily minimum of coldest month   2.29 (21.4)***     
Elevation       0.997 (29.7)**
Log distance to perennial water (m)       0.56 (21.6)***
Log distance to perennial/non-perennial water (m)       0.72 (30.5)**
Land cover (binary; moist versus dry areas)       4.76 (25.5)***
Month of survey (binary; peak season April/May versus rest of year)       8.67 (29.4)***
  1. ‡ The co-efficients, not the Odds Ratios, are shown, as the unit is a fraction, and the Odds Ratio near zero (= exp(co-efficient)).
  2. § Radiance units for NDVI (fractions from 0 to 1) are translated to a byte-compatible scale from 1 to 256.