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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