Analysis method for providing a diagnostic on the functioning of a real system, the method being based on the use of a model of the said system, where the said model includes at least two variables associated with sensors of the real system and divided into one or more groups and stored in first means for storing data, each of the said groups being defined by, and including, one or more variables called characteristic variables and grouping together all the other variables, called influent variables, having a direct or indirect influence on the value of at least one of the said characteristic variables of the said group, characterised in that it includes: - a step for initialisation of the model into a state corresponding to a given state of the real system via first processing means which communicate with the real system by a communication interface, - a step for creating a list, called the discordant variables list, of characteristic variables whose value predicted by the model is not verified in said real system, and for storing said discordant variables list in second means for storing data, via means for comparing which communicate with the real system by the communication interface, this step for creating the discordant variables list comprising: i. a step for prediction by the model of the state of the real system from a given command, ii. a step for comparison of the predicted state with the real state of the system after performing said given command, and for each characteristic variable of the said discordant variables list, a process that includes: - a step for creating a list, called initial suspect variables list, of influent variables that may have generated the discordant value of the said discordant variable, and storing said initial suspect variables list in third means for storing data, via means for selection, - a step for creating a list, called restricted list of suspect variables, by filtration of the said initial list of suspect variables, and storing said restricted list of suspect variables in fourth means for storing data, via means for filtration. - a step for initialisation of the model into a state corresponding to a given state of the real system via first processing means which communicate with the real system by a communication interface, - a step for creating a list, called the discordant variables list, of characteristic variables whose value predicted by the model is not verified in said real system, and for storing said discordant variables list in second means for storing data, via means for comparing which communicate with the real system by the communication interface, this step for creating the discordant variables list comprising: i. a step for prediction by the model of the state of the real system from a given command, ii. a step for comparison of the predicted state with the real state of the system after performing said given command, i. a step for prediction by the model of the state of the real system from a given command, ii. a step for comparison of the predicted state with the real state of the system after performing said given command, - a step for creating a list, called initial suspect variables list, of influent variables that may have generated the discordant value of the said discordant variable, and storing said initial suspect variables list in third means for storing data, via means for selection, - a step for creating a list, called restricted list of suspect variables, by filtration of the said initial list of suspect variables, and storing said restricted list of suspect variables in fourth means for storing data, via means for filtration.