16. A computer-implemented method of constructing a numerical model to measure a user's comprehension of subject matter of a text as presented in a summary of the text constructed by a user, the method comprising: specifying a numerical model associated with a given text, the numerical model comprising a first variable and an associated first weighting factor, the first variable indicative of a similarity between a summary of the given text constructed by a user and a given reference summary, a second variable and an associated second weighting factor, the second variable indicative of a degree to which a single sentence of the summary summarizes an entirety of the given text, and a third variable and an associated third weighting factor, the third variable indicative of a degree of copying in the summary of multi-word sequences present in the given text; receiving a plurality of reference summaries for the given text, each reference summary having been given a reference score, the reference summaries spanning a range of reference scores reflecting varying degrees of comprehension of the subject matter of the given text, the reference summaries having been accepted as usable for training the numerical model; training the numerical model with a processing system using the reference summaries and the given reference scores to determine values for each of the first, second and third weighting factors; and configuring the numerical model with the determined values of the first, second and third weighting factors to receive a first numerical measure, a second numerical measure and a third numerical measure for the first variable, second variable and third variable, respectively, of an actual summary to be scored so as to generate a score for the actual summary that is indicative of the user's comprehension of the subject matter of the text as presented in a summary of the text.
17. The computer-implemented method of claim 16 , wherein the training comprises: processing each of the reference summaries to determine for each reference summary a first numerical measure indicative of a similarity between the summary and a particular reference summary, the particular reference summary having been designated as representative of the subject matter of the text, a second numerical measure indicative of a degree to which a single sentence of the reference summary summarizes an entirety of the text, and a third numerical measure indicative of a degree of copying in the reference summary of multi-word sequences present in the text; and conducting a numerical regression analysis based on the first, second and third numerical measures and reference score for each of the plurality of reference summaries to determine the first, second and third weighting factors.