import { ExamGrader } from "../ExamGrader";
export declare class GradedStats {
    readonly numFullyGraded: number;
    readonly mean: number;
    readonly stddev: number;
    /**
     * Maps from question-id to mean grade on that question
     */
    private readonly gradedQuestionsMeans;
    /**
     * Maps from question-id, question-id to covariance.
     * e.g. index at ["question_id_1"]["question_id_2"] to
     * get the covariance between grades on those questions.
     */
    private readonly gradedQuestionCovarianceMatrix;
    recompute(examGrader: ExamGrader): void;
    questionMean(question_id: string): number | undefined;
    questionStddev(question_id: string): number | undefined;
    questionCovariance(question_id_1: string, question_id_2: string): number | undefined;
}