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. 1996 Nov 12;93(23):13416–13420. doi: 10.1073/pnas.93.23.13416

Table 1.

Decomposition of mean earnings difference between experimental controls and comparison sample of eligible nonparticipants

Quarter (2) Mean earnings difference (B̂) (3) Nonoverlapping support*(B̂1) [%] (4) Different density weighting (B̂2) [%] (5) Selection bias (B̂3) [%] (6) Average bias (Inline graphicSP) (7) Selection bias (Inline graphicSP) as a % of treatment impact†
Adult men, experimental controls, and comparison sample of eligible nonparticipants‡
t = 1 −418 240 −676  18 36 713
(38) (29) [−57] (35) [162] (26) [−4]
t = 2 −349 294 −658 15 30 83
(47) (37) [−84] (43) [188] (31) [−4]
t = 3 −337 305 −649 7 13 23
(55) (38) [−90] (44) [192] (30) [−2]
t = 4 −286 323 −644 35 69 117
(57) (37) [−113] (47) [225] (32) [−12]
t = 5 −305 320 −671 45 89 201
(57) (39) [−105] (52) [220] (38) [−15]
t = 6 −328 303 −655 24 47 78
(63) (44) [−93] (50) [200] (42) [−7]
 Postprogram −337 298 −659 24 48 109
  average (47) (35) [−88] (42) [195] (28) [−7]
Adult women, experimental controls, and comparison sample of eligible nonparticipants§
t = 1 −26 83 −144 35 46 302
(24) (11) [−316] (18) [548] (24) [−132]
t = 2 29 100 −120 49 64 261
(25) (13) [344] (20) [−411] (28) [167]
t = 3 38 105 −120 54 70 151
(26) (14) [272] (22) [−312] (30) [139]
t = 4 55 108 −107 54 70 206
(30) (16) [195] (23) [−193] (29) [97]
t = 5 62 117 −102 47 62 212
(34) (18) [188] (25) [−164] (33) [76]
t = 6 40 122 −114 33 44 158
(36) (18) [301] (24) [−283] (29) [82]
 Postprogram 33 106 −118 45 59 202
  average (26) (13) [318] (20) [−355] (26) [136]

Bootstrapped standard errors are shown in parentheses; percentages of mean difference attributable to components are shown in square brackets. Quarterly earnings expressed in monthly dollars. 

*

Two percent trimming rule used to determine overlapping support region (SP) following [12]. For adult males, proportion of controls in SP = 0.51. Proportion of eligible nonparticipants in SP = 0.97. For adult females, proportion of controls is 0.76 and proportion of nonparticipants is 0.96. 

†

Ratio of absolute value of Inline graphicSP to absolute value of experimentally determined impact. 

‡  Adult male sample contains 508 controls and 388 eligible nonparticipants. 

§

Adult female sample contains 696 controls and 866 eligible nonparticipants.