Credibility theory is a branch of actuarial mathematics concerned with determining risk premiums. It is employed to combine multiple estimates into a summary estimate that takes into account information on the accuracy of the initial estimates. For example, in group health insurance an insurer is interested in calculating the risk premium, ${\displaystyle RP}$, (i.e. the theoretical expected claims amount) for a particular employer in the coming year. The insurer will likely have an estimate of historical overall claims experience, ${\displaystyle x}$, as well as a more specific estimate for the employer in question, ${\displaystyle y}$. Assigning a credibility factor, ${\displaystyle z}$, to the overall claims experience (and the reciprocal to employer experience) allows the insurer to get a more accurate estimate of the risk premium in the following manner: