1. A system for receiving input specifying at least two parameter values for determining a weight of a factor for making a decision, the system comprising: an output device, for displaying a movable control element at an initial position, the initial position having at least two coordinates, each coordinate corresponding to a parameter for determining a weight of the factor; a user input device, for receiving user input to move the movable control element; and a processor, for, responsive to the user input: causing the output device to move the movable control element to a new position, the new position having at least two coordinates; causing the output device to display a visual representation of a factor weight, the visual representation having attributes determined by the coordinates of the new position of the movable control element; determining a value for a first parameter based on a first coordinate of the new position of the movable control element; determining a value for a second parameter based on a second coordinate of the new position of the movable control element; determining a value for the factor weight based on a mathematical function combining the first and second parameter values; and assigning the factor weight to the factor.