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Table 2 Patient characteristics associated with accuracy of syndrome definitions based on physician claims (OR >1.00 means the encounter characteristic increased the PPV of the syndrome definition, OR < 1.00 means the encounter characteristic reduced the PPV)

From: Patient, physician, encounter, and billing characteristics predict the accuracy of syndromic surveillance case definitions

  No. visits with a syndrome-positive physician claim Bivariate regression analysis Multivariate regression analysis1
Patient characteristics Syndrome-positive in the chart
(N = 2,967)
Syndrome-negative in the chart
(N = 1,363)
Total
(N = 4,330)
OR 95% CI P value OR 95% CI P value
  No. % No. % No. %       
Sex:             
   Female 1,810 61.0 824 60.5 2,634 60.8 Ref. Ref. Ref. Ref. Ref. Ref.
   Male 1,157 39.0 539 39.5 1,696 39.2 0.98 (0.86, 1.12) 0.75 0.89 (0.77, 1.03) 0.11
Material deprivation index:2             
   1st quintile (least deprived) 524 17.7 284 20.8 808 18.7 Ref. Ref. Ref. Ref. Ref. Ref.
   2nd quintile 584 19.7 270 19.8 854 19.7 1.16 (0.94, 1.42) 0.16 1.18 (0.95, 1.46) 0.14
   3rd quintile 604 20.4 243 17.8 847 19.6 1.33 (1.08, 1.64) 0.01 1.44 (1.15, 1.81) < 0.01
   4th quintile 581 19.6 261 19.1 842 19.4 1.21 (0.98, 1.49) 0.07 1.25 (1.01, 1.55) 0.04
   5th quintile (most deprived) 545 18.4 255 18.7 800 18.5 1.16 (0.94, 1.43) 0.16 1.21 (0.97, 1.50) 0.09
Social deprivation index:2             
   1st quintile (least deprived) 611 20.6 251 18.4 862 19.9 Ref. Ref. Ref. Ref. Ref. Ref.
   2nd quintile 574 19.3 263 19.3 837 19.3 0.90 (0.73, 1.10) 0.30 0.91 (0.74, 1.13) 0.41
   3rd quintile 572 19.3 251 18.4 823 19.0 0.91 (0.74, 1.13) 0.41 0.97 (0.77, 1.21) 0.76
   4th quintile 554 18.7 261 19.1 815 18.8 0.87 (0.70, 1.07) 0.19 0.88 (0.70, 1.10) 0.26
   5th quintile (most deprived) 527 17.8 287 21.1 814 18.8 0.75 (0.61, 0.93) 0.01 0.76 (0.60, 0.95) 0.02
Deprivation indices missing:             
   No 2,838 95.7 1,313 96.3 4,151 95.9 Ref. Ref. Ref. Ref. Ref. Ref.
   Yes 129 4.3 50 3.7 179 4.1 1.04 (0.73, 1.49) 0.83 1.06 (0.68, 1.64) 0.81
  Mean SD Mean SD Mean SD       
Age (age per 5 years is used in the regression analyses)3 36.4 24.9 43.2 24.0 38.5 24.8 0.95 (0.93, 0.96) < 0.0001 0.96 (0.94, 0.97) < 0.0001
Health services utilization (no. ambulatory care visits in the previous year)4 9.0 10.1 10.6 12.7 9.5 11.0 0.99 (0.98, 0.99) < 0.0001 0.99 (0.99, 1.00) 0.08
Charlson comorbidity index (per 1-point increase)4 0.38 0.98 0.49 1.17 0.42 1.04 0.92 (0.86, 0.97) < 0.01 0.98 (0.92, 1.05) 0.58
  1. 1 Multivariate analysis adjusted for all patient characteristics in Table 2, all physician characteristics in Table 1, and all encounter characteristics in Table 3
  2. 2 The material and social deprivation indices were calculated using Statistics Canada's 2006 census data. These indices were developed by the Quebec National Public Health Institute. The material deprivation index summarizes information on the proportion of persons who have no high school diploma, the proportion of persons employed, and the average income in the patient's 6-digit postal code area of residence. The social deprivation index summarizes information on the proportion of single-parent families, the proportion of persons living alone, and the proportion of persons separated, divorced, or widowed in the patient's 6-digit postal code area of residence.
  3. 3 On October 1st of the study year when the visit took place. The study spanned 2 years: October 1, 2005 to September 30, 2006, and October 1, 2006 to September 30, 2007.
  4. 4 Based on all medical services claims billed by all Quebec physicians (not only the 3,600 study physicians) in the year prior to the date of the syndrome-positive visit.