Estimates statistically significant marker combination values within
which one immunologically distinctive group (i.e., disease case) is more associated than
another group (i.e., healthy control), successively, using various combinations (i.e.,
"gates") of markers to examine features of cells that may be different between
groups. For a two-group comparison, the 'gateR' package uses the spatial relative risk
function that is estimated using the 'sparr' package. Details about the 'sparr' package
methods can be found in the tutorial: Davies et al. (2018)