Validity and reliability of forensic firearm examiners
6WXG\GHVLJQ
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
6WXG\GHVLJQ
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
'RHVWKHFRPSDULVRQSURYLGHVXSSRUWWKDWWKHVWULDWLRQVLQWKHFDUWULGJHFDVHV DUHWKHUHVXOWRIILULQJWKHFDUWULGJHFDVHVZLWKRQHRUZLWKWZR*ORFNSLVWROV" :KDWLV\RXUMXGJHGGHJUHHRIVXSSRUWIRUWKLVFRQFOXVLRQ"
7KHILUVWTXHVWLRQUHVXOWHGLQDVRXUFHFKRLFHZKHUHWKHSDUWLFLSDQWVMXGJHGZKHWKHU WKHFRPSDULVRQLPDJHSURYLGHVVXSSRUWIRUWZRFDUWULGJHFDVHVKDYLQJEHHQILUHG ZLWKRQH*ORFNSLVWRO VDPHVRXUFH RUZLWKWZR*ORFNSLVWROV GLIIHUHQWVRXUFH )RUWKHVHFRQGTXHVWLRQWKHSDUWLFLSDQWVZHUHDVNHGWRDVVLJQDGHJUHHRIVXSSRUW IRUWKHLUVRXUFHMXGJPHQWRQDVL[VWHSYHUEDOVFDOH 7DEOH 7KHSDUWLFLSDQWVZKR VWDWHGWKDWWKH\UHSRUWWKHLUUHVXOWVDVDQ/5LQFDVHZRUNUHFHLYHGWKHVDPHYHUEDO VFDOH EXW GHILQHG E\ QXPHULFDO IUHTXHQF\ RI RFFXUUHQFH UDQJHV HJ PRGHUDWH VXSSRUW LQWRLQWHVWILUHV )RUVDPHVRXUFHMXGJPHQWVSDUWLFLSDQWVZHUH DVNHGWRDVVXPHWKHRSSRVLWHWKDWWKHFDUWULGJHFDVHRQWKHULJKWZDVDFWXDOO\ILUHG ZLWKDQRWKHU*ORFNSLVWRO.HHSLQJWKDWDVVXPSWLRQLQPLQGWKH\ZHUHDVNHGLQHYHU\ KRZPDQ\WHVWVKRWVIURPRWKHU*ORFNSLVWROV &ROXPQ WKH\ZRXOGH[SHFWWRILQG WKHVDPHVWULDWLRQSDWWHUQ DQGUHVXOWLQJGHJUHHRIVLPLODULW\ )RUGLIIHUHQWVRXUFH MXGJPHQWVSDUWLFLSDQWVZHUHDJDLQDVNHGWRDVVXPHWKHRSSRVLWHWKDWWKHFDUWULGJH FDVHRQWKHULJKWZDVDFWXDOO\ILUHGZLWKWKHVDPH*ORFNSLVWRODVWKHRQHRQWKHOHIW .HHSLQJWKDWDVVXPSWLRQLQPLQGWKH\ZHUHDVNHGIRUKRZPDQ\WHVWVKRWVIURPWKDW *ORFNSLVWRO &ROXPQ WKH\ZRXOGH[SHFWWRILQGWKHVDPHVWULDWLRQSDWWHUQ DQG UHVXOWLQJORZGHJUHHRIVLPLODULW\ DVVHHQLQWKHFDUWULGJHFDVHRQWKHULJKW7KHVH MXGJHGIUHTXHQFLHVRIRFFXUUHQFHZHUHXVHGWRDSSUR[LPDWHWKHUHVXOWLQJ/5VDVD UDQGRPPDWFKHTXLYDOHQW> @ 7DEOH )RUVDPHVRXUFHMXGJPHQWVWKHVHSVHXGR /5VDUHFDOFXODWHGE\VHWWLQJWKHOLNHOLKRRGRIWKHGHJUHHRIVLPLODULW\JLYHQWKHVDPH VRXUFH SURSRVLWLRQ WR DQG GLYLGLQJ WKDW E\ WKH MXGJHG UHODWLYH IUHTXHQF\ RI RFFXUUHQFHRIILQGLQJWKHVDPHVWULDWLRQSDWWHUQ DQGUHVXOWLQJGHJUHHRIVLPLODULW\ ZLWK WHVW VKRWV IURP RWKHU *ORFN SLVWROV GLIIHUHQWVRXUFH SURSRVLWLRQ )RU GLIIHUHQWVRXUFH MXGJPHQWV WKH SVHXGR /5V DUHFDOFXODWHG E\GLYLGLQJ WKH MXGJHG UHODWLYHIUHTXHQF\RIRFFXUUHQFHRIILQGLQJWKHVDPHVWULDWLRQSDWWHUQ DQGUHVXOWLQJ GHJUHHRIVLPLODULW\ ZKHQWKHFDUWULGJHFDVHVZHUHILUHGZLWKWKHVDPHILUHDUP VDPH VRXUFHSURSRVLWLRQ E\WKHOLNHOLKRRGRIWKHGHJUHHRIVLPLODULW\JLYHQWKHGLIIHUHQW VRXUFH SURSRVLWLRQ ZKLFK ZDV VHW WR 7KH FKRLFH ZDV PDGH WR XVH WKHVH DSSUR[LPDWHG /5V EHFDXVH DVNLQJ WKH H[DPLQHUV WR SURYLGH WKH OLNHOLKRRG RI WKH GHJUHHVRIVLPLODULW\JLYHQHDFKRIWKHSURSRVLWLRQVZRXOGKDYHUHVXOWHGLQD WRR FRPSOH[TXHVWLRQQDLUHLQFUHDVLQJWKHOLNHOLKRRGRIPLVXQGHUVWDQGLQJRIWKHWDVNDQG GLVWRUWLRQRIWKHUHVXOWV
7KHWKLUGTXHVWLRQZDVZKHWKHUSDUWLFLSDQWVZRXOGIHHOFRQILGHQWWRUHSRUW WKHLUMXGJPHQWDERXWWKHVRXUFH LQ FDVHZRUNRUZRXOG SURYLGHDQ ´LQFRQFOXVLYHµ FRQFOXVLRQ7KHRUGHULQZKLFKWKHFRPSDULVRQLPDJHVZHUHVKRZQZDVUDQGRPL]HG
)LJXUH2YHUYLHZRIQLQHFRPSDULVRQLPDJHVVKRZLQJIHDWXUHVZLWKYDULRXVGHJUHHVRIVLPLODULW\ 7KHFRPSDULVRQVZHUHVHOHFWHGIURPWKHUDQJHRIFRPSDULVRQVFRUHVUHVXOWLQJIURPWKHFRPSXWHU EDVHG PHWKRG 7KHVH FRPSDULVRQ LPDJHV ZHUH QRW SDUW RI WKH FRPSDULVRQ LPDJHV XVHG WR DFTXLUHWKHH[DPLQHUMXGJPHQWV
IRUHDFKVXEMHFWDQGZKHQMXGJLQJWKHGHJUHHRIVLPLODULW\DQGMXGJLQJWKHVRXUFH DQGGHJUHHRIVXSSRUWSHUSDUWLFLSDQW
7DEOH7KHVFDOHXVHGWRMXGJHWKHGHJUHHRIVXSSRUWIRUWKHVDPHVRXUFHRUGLIIHUHQWVRXUFH MXGJPHQWV &ROXPQ 7KH SDUWLFLSDQWV WKDW UHSRUW /5V LQ FDVHZRUN ZHUH DOVR VKRZQ WKH LQIRUPDWLRQ LQ &ROXPQ 7KH DSSUR[LPDWHG /5V EDVHG RQ UDQGRP PDWFK HTXLYDOHQWV IRU WKH VDPHVRXUFHDQGGLIIHUHQWVRXUFHMXGJPHQWVDUHVKRZQLQ&ROXPQDQGUHVSHFWLYHO\
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
PHWKRGVVHFWLRQ :HVHOHFWHGDUHODWLYHO\ODUJHSURSRUWLRQRIORZ/5VIRUVDPHVRXUFH FRPSDULVRQV DQG KLJK /5V IRU GLIIHUHQWVRXUFH FRPSDULVRQV WR HQVXUH DQ HTXDO GLVWULEXWLRQ RI FRPSDULVRQV ZLWK YDU\LQJ /5V LQ WKH WHVW VHW )XUWKHUPRUH ZH LQFOXGHGDOOWKUHHVDPHVRXUFHFRPSDULVRQVZKHUHWKHFDOFXODWHG/5 EDVHGRQ' DQGRU'PHDVXUHPHQW ZDVVPDOOHUWKDQDQGWHQGLIIHUHQWVRXUFHFRPSDULVRQV ZKHUHWKHFDOFXODWHG/5ZDVODUJHUWKDQ PLVOHDGLQJHYLGHQFH 7KLVUHVXOWHGLQDQ RYHUUHSUHVHQWDWLRQRI´GLIILFXOWµ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