PhecapSurrogate: Define a Surrogate Variable used in Surrogate-Assisted...
In PheCAP: High-Throughput Phenotyping with EHR using a Common Automated Pipeline

Define a surrogate varible from existing features, and specify associated lower and upper cutoffs.

1	PhecapSurrogate(variable_names, lower_cutoff = 1L, upper_cutoff = 10L)

`variable_names`	a character scalar or vector consisting of variable names. If a vector is given, the value of the surrogate is defined as the sum of the values of each variable.
`lower_cutoff`	a numeric scalar. If the surrogate value of a patient is less than or equal to this cutoff, then this patient is treated as a control in SAFE.
`upper_cutoff`	a numeric scalar. If the surrogate value of a patient is greater than or equal to this cutoff, then this patient is treated as a case in SAFE.