function factory( c ) {
	var k;
	if (
		isnan( c ) ||
		c <= 0.0
	) {
		return constantFunction( NaN );
	}
	k = log1p( c );
	return pdf;

	/**
	* 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>
	*/
	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 );
	}
}
Returns a function for evaluating the probability density function (PDF) for a Bradford distribution with shape parameter `c`.

@param {PositiveNumber} c - shape parameter
@returns {Function} PDF

@example
var pdf = factory( 5.0 );
var y = pdf( 0.5 );
// returns ~0.797

y = pdf( 1.0 );
// returns ~0.465