settings.php

<?php
/**
 * Class for adding a link tracking to the options-general.php page
 */
class Add_Settings_Field {

	/**
	 * Class constructor
	 */
	public function __construct() {
		add_filter( 'admin_init' , array( &$this , 'register_fields' ) );
	}

	/**
	 * Add new fields to wp-admin/options-general.php page
	 */
	public function register_fields() {
		register_setting( 'general', 'outbound_tracking', 'esc_attr' );
		add_settings_field(
			'fav_color',
			'<label for="outbound_tracking">' . __( 'Track Outbound Links' , 'outbound_tracking' ) . '</label>',
			array( &$this, 'fields_radio' ),
			'general'
		);
	}

	/**
	 * HTML for extra settings
	 */
	public function fields_radio() {
		$value = get_option( 'outbound_tracking', '' );
		echo '<input type="radio" id="outbound_tracking_no" name="outbound_tracking" value="no"'.(strlen(esc_attr( $value )) == 0 || esc_attr( $value ) == 'no'?' checked':'' ).' /> No <input type="radio" id="outbound_tracking_yes" name="outbound_tracking" value="yes"'.(esc_attr( $value ) == 'yes'?' checked':'' ).' /> Yes ';
	}

}
new Add_Settings_Field();
?>