Randomisation by cluster and the problem of social class bias.
1989 ◽
Vol 43
(1)
◽
pp. 29-36
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Keyword(s):
2009 ◽
Vol 4
(3)
◽
pp. 61-97
◽
Keyword(s):
2004 ◽
Vol 74
(1)
◽
pp. 62-73
◽
Keyword(s):