Foren­sic science’s un­cer­tain­ties

The Washington Post Sunday - - SUNDAY OPINION -

Re­gard­ing the May 30 news ar­ti­cle “FBI dis­closes er­rors in DNA anal­y­sis”:

Shaken baby syn­drome, foren­sic hair anal­y­sis and now DNA match prob­a­bil­i­ties may have been rou­tinely over­stated by pros­e­cu­tion wit­nesses, po­ten­tially lead­ing to wrong­ful con­vic­tions and in­car­cer­a­tions and per­haps even ex­e­cu­tions.

Why do courts al­low th­ese mat­ters to be pre­sented to ju­ries as mat­ters of sci­en­tific fact? They are not. They have not been em­pir­i­cally proved us­ing the sci­en­tific method.

The vast body of tech­ni­cal, sci­en­tific and med­i­cal tes­ti­mony is not amenable to sci­en­tific proof but is merely con­sen­sus of opin­ion among prac­ti­tion­ers, and some­times not even that. It re­mains within the realm of the­ory. Pro­po­nents of such pseudo-sci­en­tific tes­ti­mony are dis­in­clined to ad­mit this and apt to over­state its re­li­a­bil­ity. Op­pos­ing lawyers are ill-equipped to force such an ad­mis­sion as it en­tails chal­leng­ing an ex­pert wit­ness in his or her field of ex­per­tise. Their only re­al­is­tic op­tion is to present an op­pos­ing ex­pert, leav­ing a jury to toss a coin as to which one to be­lieve — with some­one’s life or lib­erty hang­ing in the bal­ance. There has to be a bet­ter way.

Paul B. Weiss, Hedgesville, W.Va.

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