Serum sodium concentration <= 135 mmol/liter
1 = na > 135
2 = na <= 135

1 = male
2 = female

Urine output
1 = <3
2 = >=3

Self-reported fluid intake
1 = Every mile
2 = Every other mile
3 = Every third mile or less often

Self-reported water loading
1 = No
2 = Yes

1 = 3.0 to 4.9
2 = 2.0 to 2.9
3 = 1.0 to 1.9
4 = 0.0 to 0.9
5 = -1.0 to -0.1
6 = -2.0 to -1.1
7 = -5.0 to -2.1