Specification of a time is received from a device that uses an in-home-presence probability calculation system, a probability that a person is at home at the specified time is calculated on the basis of a specified operation time and a specified correlation when the specified operation time is a time within a period of a certain time ending at the time at which the specification has been received, and information as to whether or not a person is at home is output to the device on the basis of the calculated probability.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. An in-home-presence probability calculation method used in an in-home-presence probability calculation system that provides information as to whether or not a person is at home, the in-home-presence probability calculation method comprising: receiving operation information on a device arranged in a home via a network every time a certain operation is performed for the device; specifying operation times at which the certain operation has been performed, in accordance with the received operation information; receiving, every time a state is entered in which it is expected that no one is at home, time information of a time at which the state has been entered; specifying in-home-absence times at which a state has been entered in which it is expected that no one is at home, in accordance with the received time information; specifying a correlation between a set including the specified operation times and a set including the specified in-home-absence times; receiving specification of a time from a device that uses the in-home-presence probability calculation system; calculating, when a specified operation time among the specified operation times is a time within a period of a certain time ending at the time at which the specification has been received, a probability that a person is at home at the specified time on the basis of the specified operation time and the specified correlation; and outputting the information as to whether or not a person is at home to the device that uses the in-home-presence probability calculation system on the basis of the calculated probability. 2. The in-home-presence probability calculation method according to claim 1, wherein time differences are calculated for the specified operation times, each of the time differences being the difference between a corresponding one of the specified operation times and an in-home-absence time that is first specified within a period from the corresponding one of the specified operation times, the period satisfying a certain condition, and the correlation is specified using a frequency distribution of the calculated time differences. 3. The in-home-presence probability calculation method according to claim 2, wherein the specified correlation is a cumulative frequency distribution of the time differences. 4. The in-home-presence probability calculation method according to claim 3, wherein the certain operation is an operation for turning off a main power switch of the device arranged in the home. 5. The in-home-presence probability calculation method according to claim 4, wherein the device arranged in the home is one of a plurality of devices arranged in the home, target devices, whose main power switch are to be turned off, are specified among the plurality of devices, correlations are specified only for the target devices, a correlation is specified having a strength that satisfies a certain condition among the specified correlations, and the probability is calculated using the specified correlation that satisfies the certain condition. 6. The in-home-presence probability calculation method according to claim 3, wherein the certain operation is one of a plurality of certain operations, correlations are specified for the certain operations, each of the correlations being specified for a corresponding one of the certain operations, a correlation is specified having a strength that satisfies a certain condition among the specified correlations, and the probability is calculated using the specified correlation that satisfies the certain condition. 7. A server apparatus that provides information as to whether or not a person is at home, the server apparatus comprising: a first receiving unit that receives operation information on a device arranged in a home via a network every time a certain operation is performed for the device and that receives, every time a state is entered in which it is expected that no one is at home, time information of a time at which the state has been entered; an operation time specification unit that specifies an operation times at which the certain operation has been performed, in accordance with the received operation information; an in-home-absence time specification unit that specifies in-home-absence times at which a state has been entered in which it is expected that no one is at home, in accordance with the received time information; a correlation specification unit that specifies a correlation between a set including the specified operation times by the operation time specification unit and a set including the specified in-home-absence times by the in-home-absence time specification unit; a second receiving unit that receives specification of a time from a device that uses the server apparatus; and a probability calculation unit that calculates, when a specified operation time among the specified operation times by the operation time specification unit is a time within a period of a certain time ending at the time at which the specification has been received, a probability that a person is at home at the specified time on the basis of the specified operation time and the specified correlation, wherein, the information as to whether or not a person is at home is output to the device that uses the server apparatus on the basis of the calculated probability, and wherein, one of the first receiving unit, the operation time specification unit, the in-home-absence time specification unit, the correlation specification unit, the second receiving unit, and the probability calculation unit includes a processor. 8. An in-home-presence probability calculation system that provides information as to whether or not a person is at home, the in-home-presence probability calculation system comprising: a server apparatus comprising, a first receiving unit that receives operation information on a device arranged in a home via a network every time a certain operation is performed for the device and that receives, every time a state is entered in which it is expected that no one is at home, time information of a time at which the state has been entered; an operation time specification unit that specifies operation times at which the certain operation has been performed, in accordance with the received operation information; an in-home-absence time specification unit that specifies in-home-absence times at which a state has been entered in which it is expected that no one is at home, in accordance with the received time information, a correlation specification unit that specifies a correlation between a set including the specified operation times by the operation time specification unit and a set including the specified in-home-absence times by the in-home-absence time specification unit; a second receiving unit that receives specification of a time from a device that uses the server apparatus; and a probability calculation unit that calculates, when a specified operation time among the specified operation times by the operation time specification unit is a time within a period of a certain time ending at the time at which the specification has been received, a probability that a person is at home at the specified time on the basis of the specified operation time and the specified correlation, wherein, the information as to whether or not a person is at home is output to the device that uses the server apparatus on the basis of the calculated probability, and wherein, one of the first receiving unit, the operation time specification unit, the in-home-absence time specification unit, the correlation specification unit, the second receiving unit, and the probability calculation unit includes a processor.