1. A computer-implemented method of measuring a user's English language proficiency, the method comprising: receiving a constructed response generated by a user, the constructed response being based on a picture; parsing the constructed response with a processing system to generate a set of individual words associated with the constructed response; processing the constructed response with the processing system to identify in the constructed response a plurality of multi-word sequences, each multi-word sequence comprising a sequence of two or more adjacent words in the constructed response; processing the constructed response with the processing system to determine a first numerical measure indicative of a presence of one or more grammar errors in the constructed response; processing the set of individual words and a reference corpus with the processing system to determine a second numerical measure indicative of a degree to which the constructed response describes a subject matter of the picture, each word of the set of individual words being compared to individual words of the reference corpus to determine the second numerical measure, the reference corpus having been designated as representative of the subject matter; processing the plurality of multi-word sequences of the constructed response and an n-gram dataset comprising a plurality of entries with the processing system to determine a third numerical measure indicative of a degree of awkward word usage in the constructed response, each of the multi-word sequences of the constructed response being searched across the entries of the n-gram dataset to determine the third numerical measure, wherein each entry of the n-gram dataset includes an English word n-gram and an associated statistical association score, the searching of each multi-word sequence comprising comparing the multi-word sequence of the constructed response to English word n-grams of the n-gram dataset to determine a matching entry of the n-gram dataset, the statistical association score for the matching entry indicating a probability of the multi-word sequence appearing in a well-formed text; and applying a numerical, computer-based scoring model to the first numerical measure, the second numerical measure, and the third numerical measure to automatically determine a score for the constructed response indicative of the user's English language proficiency, the numerical, computer-based scoring model including a first variable and an associated first weighting factor, the first variable receiving a value of the first numerical measure, a second variable and an associated second weighting factor, the second variable receiving a value of the second numerical measure, and a third variable and an associated third weighting factor, the third variable receiving a value of the third numerical measure.