My 2 cents : If you have no ground in your bathroom, just a black and white wire in the outlet box, You can install a Ground Fault Circuit Interruptor and connect the wires to the appropriate screws ( Line side ) . This is a perfectly acceptable method of installing a GFCI in a bathroom per the National Electrical Code.. The GFCI senses an imbalance of current of approximately 6 milli amperes, between the Hot leg and the Neutral Leg. Although a ground is preferred in a replacement installation, it is not necessary when replacing a GFCI outlet.