ABSTRACT
Lifetimes in hours (h) are given in Table 79.1 for 417 (40 W) internally frosted incandescent bulbs from 42-weekly quality control tests to failure [1,2]. Each week, 10 samples were selected from that week’s manufacture. This procedure was followed for a total of 42 weeks in the year 1947. Three failure times were not recorded. With close control of the mature manufacturing processes and testing conditions, a normal probability distribution was expected [1]. Failure Times (Hours) for 417 Light Bulbs
225
836
930
985
1037
1103
1170
1243
521
844
931
985
1039
1104
1170
1248
525
854
932
985
1040
1105
1171
1248
529
855
932
985
1045
1105
1172
1250
609
856
932
990
1049
1106
1172
1252
610
856
932
990
1054
1106
1173
1254
612
858
932
990
1055
1107
1173
1255
621
860
933
992
1055
1109
1176
1258
623
862
934
995
1056
1110
1176
1262
653
863
935
996
1056
1112
1178
1272
658
867
935
996
1057
1113
1180
1277
666
872
935
998
1058
1115
1181
1277
675
878
936
999
1058
1116
1184
1289
699
880
938
1000
1061
1117
1185
1292
702
880
938
1000
1061
1118
1187
1297
704
883
940
1001
1062
1120
1187
1297
705
883
942
1002
1063
1121
1187
1302
709
885
943
1002
1063
1121
1188
1303
709
889
943
1002
1067
1122
1192
1303
716
890
944
1003
1067
1122
1195
1303
730
892
944
1009
1067
1122
1195
1308
732
893
946
1009
1067
1122
1196
1308
744
895
948
1009
1068
1122
1197
1310
759
896
949
1011
1069
1126
1197
1311
760
898
950
1011
1069
1127
1201
1320
765
898
951
1013
1069
1133
1202
1324
765
900
954
1014
1071
1134
1203
1324
769
900
954
1014
1075
1135
1203
1331
773
901
956
1016
1077
1137
1204
1333
775
902
956
1021
1077
1138
1209
1337
780
904
958
1022
1078
1141
1211
1340
785
905
958
1022
1078
1141
1217
1340
787
905
958
1022
1079
1143
1218
1343
788
909
960
1023
1080
1147
1220
1354
798
910
964
1023
1080
1148
1220
1358
801
912
965
1024
1081
1149
1222
1381
807
912
966
1024
1083
1150
1225
1384
811
916
968
1024
1083
1151
1225
1385
813
917
970
1024
1085
1151
1227
1385
813
918
970
1026
1085
1153
1228
1404
814
918
970
1028
1085
1156
1229
1415
816
918
972
1028
1086
1156
1230
1425
818
919
972
1029
1088
1157
1233
1430
824
920
972
1029
1091
1157
1233
1438
824
922
976
1033
1092
1157
1233
1461
824
923
976
1033
1093
1157
1234
1470
826
924
978
1034
1096
1160
1235
1485
827
924
980
1035
1096
1162
1235
1490
830
924
980
1035
1101
1165
1237
1550
831
926
983
1035
1102
1166
1240
1555
832
928
984
1037
1102
1169
1240
1562
833
929
984
1037
1103
1170
1240
1635
1690
