RESULTS: The frameworks differ in their underlying assumptions to estimate value split and data requirements. The Briggs approach does not require monotherapy data for the add-on but needs assumptions regarding market power of the backbone. The Towse framework assumes balanced market power (although weights can be changed) and requires health benefits for all components, suggesting structured expert elicitation to estimate missing evidence. With perfect information, the Towse approach attributes more value to the add-on in super-additive combinations if its monotherapy value is worse than the backbone, whereas the add-on receives more value in the Briggs framework when the combination is sub-additive. Where the added value of the combination is constant additive, the value split is equal for both frameworks. With imperfect information and balanced market power, Briggs attributes more value to add-on therapies than the Towse approach when the combination is assumed to be super-additive. When the combination is assumed to be sub-additive, the add-on receives less value in the Briggs framework.

CONCLUSIONS: Both frameworks are valuable as they promote stakeholder dialogue and engagement on this topic. Our findings demonstrate that they can lead to different conclusions depending on the available evidence. More research is needed before they are to be formally integrated in HTA and pricing negotiations.