Cochran, William Gemmell,  1909- <br/><br/>
Sampling techniques / 
William G. Cochran. 
 - Third 
 - New York :  Wiley,  c1977. 
 - xvi, 428 p. :  ill. ;  24 cm. 
 - Wiley series in probability and mathematical statistics A Wiley publication in applied statistics .