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. Implications for practice or policy: • Instructors can use our measure to evaluate their students’ effective use of online learning technologies. • Course designers can use the measure to select the right mix of online and offline delivery methods. • Educators can use the measure to determine the most effective platform for delivering introductory, substantive or review material. • Our method helps researchers compare and generalise results from existing studies of the relative performance of online and offline educational technologies.