The disclosed embodiments provide a reputation system. The reputation system includes a statistical model associated with a set of items and a set of dimensions of the items in the reputation system, wherein the statistical model is trained using a positive class and a negative class. The reputation system also includes a scoring apparatus that applies the statistical model to a set of features for each of the items to estimate a set of reputation scores for the items. Finally, the reputation system includes a ranking apparatus that enables use of the set of reputation scores in the reputation system.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A computer-implemented method for facilitating use of a reputation system, comprising: obtaining a statistical model associated with a set of users and a set of skills of the users in the reputation system, wherein the statistical model is trained using a positive class and a negative class; applying the statistical model to a set of features for each of the users to estimate a set of reputation scores for the users; populating a matrix of the users and the skills with the reputation scores and unknown values for user-skill pairs that do not have explicit reputation scores; calculating a factorization of the matrix to produce at least two factor matrices, wherein the at least two factor matrices are multiplied to generate one or more inferred values that replace the unknown values in the matrix; and obtaining a ranking of the users by one or more skills specified by a query, wherein the ranking is based on a linear combination of reputation scores associated with the one or more skills; wherein obtaining the ranking of the users includes: obtaining an inverted index of the one or more skills, using the inverted index to identify a subset of the users with reputation scores in the one or more skills, and ranking the subset of the users by the reputation scores. 2. The computer-implemented method of claim 1, further comprising: obtaining a set of training data comprising the positive class and the negative class; and using the training data to train the statistical model. 3. (canceled) 4. The computer-implemented method of claim 1, wherein the set of features comprises demographic features, social features, and behavioral features. 5. The computer-implemented method of claim 4, wherein the social features comprise one or more endorsement features. 6. The computer-implemented method of claim 5, wherein the one or more endorsement features comprise: a number of endorsers; a number of endorsements; and a ranking in an endorsement network. 7. The computer-implemented method of claim 1, wherein the positive class comprises known experts and the negative class comprises random users. 8. The computer-implemented method of claim 1, wherein the statistical model comprises a logistic regression model. 9. (canceled) 10. A reputation system, comprising: a statistical model associated with a set of users and a set of skills of the users in the reputation system, wherein the statistical model is trained using a positive class and a negative class; a scoring apparatus, operated by a computer system comprising at least a processor, configured to apply the statistical model to a set of features for each of the users to estimate a set of reputation scores for the users, wherein the set of reputation scores and unknown values for user-skill pairs that do not have explicit reputation scores are used to populate a matrix of the users and the skills; an inference apparatus configured to: calculate a factorization of the matrix to produce at least two factor matrices, wherein the at least two matrices are multiplied to generated one or more inferred values that replace the unknown values in the matrix; and a ranking apparatus configured to enable use of the set of reputation scores in the reputation system, wherein a ranking of the users is obtained by one or more skills specified by a query using the factorization of the matrix, wherein the ranking is based on a linear combination of reputation scores associated with the one or more skills; wherein obtaining the ranking of the users includes: obtaining an inverted index of the one or more skills, using the inverted index to identify a subset of the users with reputation scores in the one or more skills, and ranking the subset of the users by the reputation scores. 11. The reputation system of claim 10, further comprising: a training apparatus configured to: obtain a set of training data comprising the positive class and the negative class; and use the training data to train the statistical model. 12. (canceled) 13. The reputation system of claim 10, wherein the set of features comprises demographic features, social features, and behavioral features. 14. The reputation system of claim 13, wherein the social features comprise one or more endorsement features. 15. The reputation system of claim 10, wherein the positive class comprises known experts and the negative class comprises random users. 16. A non-transitory computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method for facilitating use of a reputation system, the method comprising: obtaining a statistical model associated with a set of users and a set of skills of the users in the reputation system, wherein the statistical model is trained using a positive class and a negative class; applying the statistical model to a set of features for each of the users to estimate a set of reputation scores for the users; populating a matrix of the users and the skills with the reputation scores and unknown values for user-skill pairs that do not have explicit reputation scores; calculating a factorization of the matrix to produce at least two factor matrices, wherein the at least two factor matrices are multiplied to generate one or more inferred values that replace the unknown values in the matrix; and obtaining a ranking of the users by one or more skills specified by a query, wherein the ranking is based on a linear combination of reputation scores associated with the one or more skills; wherein obtaining the ranking of the users includes: obtaining an inverted index of the one or more skills, using the inverted index to identify a subset of the users with reputation scores in the one or more skills, and ranking the subset of the users by the reputation scores. 17. The non-transitory computer-readable storage medium of claim 16, the method further comprising: obtaining a set of training data comprising the positive class and the negative class; and using the training data to train the statistical model. 18. (canceled) 19. The non-transitory computer-readable storage medium of claim 16, wherein the positive class comprises known experts and the negative class comprises random users. 20. (canceled) 21. The computer-implemented method of claim 1, further comprising: generating quantiles of the reputation scores in the matrix of the users and skills; and generating a ranking of the users based on closeness of the generated quantiles of the reputation scores to a plurality of quantiles specified in a query. 22. The reputation system of claim 10, wherein the statistical model comprises a logistic regression model. 23. The non-transitory computer-readable storage medium of claim 16, wherein the set of features comprises demographic features, social features, and behavioral features. 24. The non-transitory computer-readable storage medium of claim 23, wherein the social features comprise one or more endorsement features. 25. The non-transitory computer-readable storage medium of claim 16, wherein the statistical model comprises a logistic regression model.