Murthy’s method (METHOD=PPS_MURTHY) selects two units from each stratum, with probability proportional to size and without replacement. The selection probability for unit i in stratum h equals

where and

Murthy’s algorithm first selects a unit with probability . Then a second unit is selected from the remaining units with probability , where unit i is the first unit selected. The joint selection probability for units i and j in stratum h equals

See Cochran (1977, pp. 263–265) and Murthy (1957) for details.