Whether the use of lecture capture technology helps improve student performance is a contested area of research. In most cases, the answer relies on the degree to which online recordings supplement or substitute for live or live-streamed lecture delivery. We present a parameter, the technical rate of substitution, which captures this information holding student performance constant. We introduce a method to estimate this measure, which we applied to a pilot sample of students in a first-year quantitative methods class. We find imperfect substitutability: live lectures are, in the context of our sample, a less resource-intensive technology than the corresponding online recording to produce a set exam score. Our main contribution is the proposed parameter and the method to derive it. Its calculation significantly facilitates comparison and consolidation of previous research and provides valuable insights on the relative effectiveness of different learning platforms to inform instructor best practice and higher education policy.