TSP (Two-Stage Probit) is the paper's advocated estimator (in the title and abstract) and the one the paper argues is least biased; the -1.63 TSP elasticity is the headline || 'The estimated price elasticity obtained by the TSP method is smaller (in absolute value) than the OLS estimate, and exceeds the estimate obtained by the IV and 2SLS methods.' (p.1138, Summary); 'These values computed at the mean marginal price and consumption levels are, respectively, -1.63, -2.01, -1.20, and -1.61.' (p.1138)
Terza, J. (1986): “Determinants of Household Electricity Demand: A Two-Stage Probit Approach.” Southern Economic Journal 52(4), 1131-1139