Analysing the efficiency of health systems: a systematic review of the literature - Mbau, R; Musiega, A; Nyawira, L; Tsofa, B; Mulwa, A; Molyneux, S; Maina, I; Jemutai, J; Normand, C; Hanson, K; Barasa, E (Applied Health Economics and Health Policy, 2022)