An objective of the present invention is to efficiently identify a combination of other variables which contribute to variation of a target variable, and extract same as explanatory variables (factors). A factor extraction system according to the present invention defines a covariant composite variable which is configured of a combination of event variables and a binary number which represents whether the combination is present in event data, and obtains a correlation between the covariant composite variable and the target variable, thereby extracting contribution factors.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A factor extraction system for extracting a factor contributing to a target variable, the factor extraction system comprising: an event variable conversion section which converts event data describing a plurality of events constituted by a combination of one or more sets of a first component and a first element value, into event variable data describing an event variable in which a first set of the first component and the first element value is set to be a second component and a value showing by using a binary number whether an event represented by the second component is present in the event data is set to be a second element value; a covariant composite variable conversion section which converts the event variable data into covariant composite variable data describing a covariant composite variable in which a second set which combines further one or more pieces of the second component constituting the event variable is set to be a third component, and a value showing by using a binary number whether an event represented by the third component is present in the event data is set to be a third element value; and a contribution variable selection section which obtains a contribution degree of the third component to the target variable by determining a correlation between the target variable and the covariant composite variable, and which outputs the third component whose contribution degree is equal to or greater than a predetermined threshold value. 2. The factor extraction system according to claim 1, wherein the covariant composite variable conversion section performs machine learning of a correlation between the second component and the third component based on the event data, and converts a set of the second component and the second element value into a set of the third component and the third element value by identifying the third component whose correlation degree with the second component is equal to or greater than a predetermined threshold value. 3. The factor extraction system according to claim 1, wherein the event variable conversion section extracts all combinations of the first component and the first element value which are present in the event data by acquiring the first component and the first element value regarding all events written in the event data, and generates the event variable by setting all the extracted combinations to be the second component. 4. The factor extraction system according to claim 3, wherein when the first element value written in the event data is a numerical value, the event variable conversion section, by dividing the first component corresponding to the numerical value into a plurality of numerical value ranges, converts the event data into a combination of the first component and the numerical value ranges, and further, the event variable conversion section converts the numerical value into a combination of the second component and the second element value by determining which range of the plurality of numerical value ranges includes the numerical value. 5. The factor extraction system according to claim 3, wherein when the first element value written in the event data is a character string, the event variable conversion section converts the event data into a combination of the first component and the character string by extracting all the character strings that are present in the event data, and further the event variable conversion section converts the character string into a combination of the second component and the second element value by determining whether the combination of the first component and the character string is included in the event data. 6. The factor extraction system according to claim 1, wherein when the second component written in the event variable data represents a movement locus of an object to be measured in one of the events, the covariant composite variable conversion section adopts all the movement loci written in the event variable data as the third component. 7. The factor extraction system according to claim 1, further comprising: a factor label output section which outputs the third component selected by the contribution variable selection section. 8. The factor extraction system according to claim 6, further comprising: a factor label output section which outputs the third component selected by the contribution variable selection section, wherein when the third component represents the movement locus, the factor label output section outputs an image obtained by imaging the movement locus, as the third component. 9. The factor extraction system according to claim 1, wherein the covariant composite variable conversion section converts the event variable data into the covariant composite variable data by repeating machine learning of a first coupling degree between one or more pieces of the second component and the third component in a process of learning from the second component to the third component and machine learning of a second coupling degree between the third component and the second component in a process of reverse learning from the third component to the second component. 10. The factor extraction system according to claim 9, wherein the covariant composite variable conversion section reduces a number of pieces of the second component coupled to the third component in the process of machine learning of the second coupling degree by subtracting a value of the second coupling degree according to a predetermined rule, as compared with a case where no subtraction is performed. 11. A factor extraction method for extracting a factor contributing to a target variable, the factor extraction method comprising: converting event data describing a plurality of events constituted by a combination of one or more sets of a first component and a first element value, into event variable data describing an event variable in which a first set of the first component and the first element value is set to be a second component and a value showing by using a binary number whether an event represented by the second component is present in the event data is set to be a second element value; converting the event variable data into covariant composite variable data describing a covariant composite variable in which a second set which combines further one or more pieces of the second component constituting the event variable is set to be a third component, and a value showing by using a binary number whether an event represented by the third component is present in the event data is set to be a third element value; and outputting the third component whose contribution degree is equal to or greater than a predetermined threshold value by obtaining the contribution degree of the third component to the target variable by determining a correlation between the target variable and the covariant composite variable.