function pdf( x ) {
		if (
			isnan( x )
		) {
			return NaN;
		}
		if ( x < 0.0 || x > 1.0 ) {
			// Support of the Bradford distribution: [0,1]
			return 0.0;
		}
		return c / ( ( 1.0 + ( c*x ) ) * k );
	}
Evaluates the probability density function (PDF) for a Bradford distribution.

@private
@param {number} x - input value
@returns {Probability} evaluated PDF

@example
var y = pdf( 0.5 );
// returns <number>