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Table 1 Parameterization of the group variable in the multiple linear regression models

From: Fluid balance, change in serum creatinine and urine output as markers of acute kidney injury post cardiac surgery: an observational study

 

Parameterization (corresponding parameter in the model)

Group

X1 (β1)

X2 (β2)

X3 (β3)

X4 (β4)

1) SCr-, UO-, FOL-

0

0

0

0

2) SCr-, UO-, FOL+

1

0

0

0

3) SCr-, UO+, FOL-

1

1

0

0

4) SCr-, UO+, FOL+

1

1

1

0

5) SCr+

1

1

1

1

  1. Each group variable or combination of SCr/UO/FOL status was parameterized as above so that the group variable could be considered as an ordinal variable in the multiple linear regression model. β1 indicates a comparison between SCr-, UO-, FOL- and SCr-, UO-, FOL+, β2 indicates a comparison between SCr-, UO-, FOL + and SCr-, UO+, FOL- and so forth.
  2. SCr+: Meeting the criteria of Change in SCr ≥ 26.5 µmol/L; SCr -: Not meeting the Change in SCr criteria.
  3. UO+: Meeting the criteria of Urine Output ≤0.5 cc/kg/hour for greater than 6 hours; UO-: Not meeting the Urine Output criteria.
  4. FOL+: Meeting the criteria of Fluid Overload, defined as fluid balance ≥ 6.5 cc/kg; FOL-: Not meeting the Fluid Overload criteria.