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Research by ( Cooper, Brown, Gottesmann, Ayllon ) showed that sz diagnosis was ( twice, three times, many times ) as likely in America using the ( DSM, MSM, DSS, DTS ) compared to England where they used the ( ICD, ICT, ISD, CRC ). Cooper said it was ( highly unlikely, very likely, probable, definitely ) that this difference was due to ( cultural factors, social factors, genetic factors ) but rather that it was due to the ( unreliability, reliability, fact ) of having two ( different diagnostic systems, similar diagnostic systems, countries, hospital systems ). However this research was conducted in the ( 70's, 50's, 90's, 80's, 30's ) and since then efforts have been made to ( bring, push, end ) the two different systems ( closer together, further apart ), making this ( less, more, half ) of an issue.