1. A computer-implemented method for estimating an ability of a worker in a process for integrating work results of multiple workers for the same task, the method comprising: processing, by an optical character recognition (OCR) engine, character recognition task data; logging, in response to the processing, the processed character recognition task data, in a task log; receiving, by a computer system and for each of one or more tasks, a work result of the OCR engine from the task log, and a work result of a succeeding-stage worker that works based on the work result of the OCR engine estimating multiple parameters of a probability model in which an ability of the succeeding-stage worker conditioned by a quality of the work result of the OCR engine is introduced as a conditioned ability parameter, based on the multiple work results obtained for each of the one or more tasks, wherein the probability model is a generative model that includes, for each of the one or more tasks, a work result of each of one or more preceding-stage workers, including the OCR engine, as a first observed variable, a work result of each of one or more succeeding-stage workers as a second observed variable, and a work result to be obtained as a latent variable, and wherein estimating the multiple parameters comprises: calculating, for each of the one or more tasks, the work result to be obtained, based on a current value of each of the multiple parameters; calculating a new value of each of the multiple parameters based on the calculated work result to be obtained for each of the one or more tasks; and determining whether or not a convergence condition is satisfied.