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Table 1 Reasons for exclusion of potential study participants – cases vs. controls

From: Use of the i2b2 research query tool to conduct a matched case–control clinical research study: advantages, disadvantages and methodological considerations

Reason for exclusion Excluded potential cases (N = 136) Excluded potential controls (N = 406)
Inaccurate query   
  No kidney stone 28 (20.6) NA
  No G-tube 3 (2.2) 31 (7.6)
Did not meet inclusion criteria   
  Outside of study age range 42 (30.9) NA
  Outside of study time period 35 (25.7) NA
  Kidney stone/G-tube asynchronous 14 (10.3) 82 (20.2)
Inadequate clinical data 13 (9.6) 293 (72.2)
Other   
  No matching control 1 (0.73) NA