--- a/src/modules/glm/samplers/KS.h
+++ b/src/modules/glm/samplers/KS.h
@@ -4,7 +4,28 @@
 class RNG;
 
 namespace glm {
-    double sample_lambda(double delta, RNG *rng);
+    /**
+     * Utility function used by the HolmesHeld and AlbertChib sampling
+     * methods in binary logistic regression models.
+     *
+     * A variable "Z" with logistic distribution may be considered as
+     * a scale mixture of normal distributions with variance lambda,
+     * where lambda=(2*psi)^2 and "psi" has a Kolmogorov-Smirnov
+     * distribution. Given Z, this function draws a sample from the
+     * posterior distribution of lambda.
+     *
+     * Although the posterior distribution of lambda given Z cannot
+     * be expressed in closed form, it can be efficiently sampled using
+     * a series approximation as described by Devroye (1986) Non-Uniform
+     * Random Variate Generation, Springer-Verlag, New York. Note that
+     * this book is currently available for free on line at
+     * http://luc.devroye.org/rnbookindex.html
+     *
+     * @param Z value of a random variable with logistic distribution
+     *
+     * @param rng Random number generator used for sampling
+     */
+    double sample_lambda(double Z, RNG *rng);
 }
 
 #endif /* KS_H_ */