{"corpus_id":94126379,"paper_sha":"ca2b451b21b576ffb2cc5197eab45a85261cbfa5","doi":"10.1107/S0567739481001629","arxiv_id":null,"pmid":null,"pmcid":null,"mag_id":1974864349,"dblp_id":null,"acl_id":null,"title":"On the application of Hamilton's ratio test to the assignment of absolute configuration and an alternative test","year":1981,"publication_date":"1981-09-01","venue":"","journal":{"name":"Acta Crystallographica Section A","pages":"734-741","volume":"37"},"journal_issn":null,"journal_title":null,"publication_types":[],"pubmed_pub_types":null,"s2_fields_of_study":["Chemistry"],"reference_count":1,"citation_count":256,"influential_citation_count":2,"is_open_access":false,"arxiv_categories":null,"arxiv_license":null,"arxiv_journal_ref":null,"mesh_headings":null,"chemicals":null,"comments_corrections":null,"source_flags":1,"s2_open_access_pdf_url":null,"s2_open_access_landing_url":null,"s2_open_access_license":null,"s2_open_access_status":null,"pmc_open_access_pdf_url":null,"pmc_open_access_landing_url":null,"pmc_open_access_license":null,"pmc_open_access_status":null,"unpaywall_open_access_pdf_url":null,"unpaywall_open_access_landing_url":null,"unpaywall_open_access_license":null,"unpaywall_open_access_status":null,"abstract":"Examples are given of recent abuses or debatable applications of the R-factor ratio test (\\cal R) for the assignment of absolute configuration, and it is shown that some of the enhanced ratios that have been used do not necessarily imply a statistically significant reduction in α, the probability of making a wrong assignment. Reasons are given for believing α is usually seriously underestimated anyway, and that in marginal situations the weighted ratio, \\cal Rw, is a safer guide than \\cal R and can even contradict the assignment based on \\cal R. Aids are given to facilitate the estimation of α that are much easier to use than interpolation or extrapolation from Hamilton's tables [Hamilton (1965). Acta Cryst. 18, 502-510]. The misconceptions led to a re-examination of the validity of Hamilton's application of linear-hypothesis testing to this particular problem. A more rigorous justification can be achieved by expressing the atomic scattering factors of all the anomalous scatterers in a crystal in the form f0j + f'j + iηf''j and refining η, the chirality/polarity parameter. Its standard deviation offers an alternative and more realistic index of the probability of an assignment. A postscript contributed by Professor G. M. Sheldrick reports very encouraging results for η refinement of three structures.","claims":[{"public_id":"cl_aee5f2a0f3d05895cad859783ff2f3a1","status":"active","text":"In marginal situations, the weighted ratio is a safer guide than the R-factor ratio test and can even contradict the assignment based on it.","confidence":0.93,"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/claims/cl_aee5f2a0f3d05895cad859783ff2f3a1"},{"public_id":"cl_74a1ab037b76c8e60119c3a608887770","status":"active","text":"Refining the chirality/polarity parameter η after expressing anomalous scatterers as f0j + f'j + iηf''j provides a more rigorous justification and yields an alternative, more realistic index of assignment probability.","confidence":0.98,"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/claims/cl_74a1ab037b76c8e60119c3a608887770"},{"public_id":"cl_44e3ad7d06fc308d7ead4d174415181d","status":"active","text":"Some enhanced R-factor ratios used for assigning absolute configuration do not necessarily imply a statistically significant reduction in the probability of a wrong assignment.","confidence":0.96,"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/claims/cl_44e3ad7d06fc308d7ead4d174415181d"},{"public_id":"cl_275853bdf16431ac0f839218b6c94602","status":"active","text":"The probability of making a wrong assignment is usually seriously underestimated by the usual α estimates.","confidence":0.9,"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/claims/cl_275853bdf16431ac0f839218b6c94602"},{"public_id":"cl_41976c42adb7936af163e0aee3b44e4b","status":"active","text":"The standard deviation of η offers an alternative and more realistic index of the probability of an assignment.","confidence":0.95,"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/claims/cl_41976c42adb7936af163e0aee3b44e4b"}],"concepts":[{"public_id":"co_0c1d282b7b41fc6047ad67eda1da6694","status":"active","name":"chirality/polarity parameter η","description":"A refined parameter representing chirality or polarity in the anomalous-scattering model.","types":["model parameter"],"aliases":["η"],"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/concepts/co_0c1d282b7b41fc6047ad67eda1da6694"},{"public_id":"co_12ef71c6d0427bed5738eaebdac502ed","status":"active","name":"weighted ratio","description":"A weighted version of the ratio criterion used to guide absolute-configuration assignment.","types":["statistical measure"],"aliases":["Rw"],"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/concepts/co_12ef71c6d0427bed5738eaebdac502ed"},{"public_id":"co_2379559d7439f07c9e139245c56e1796","status":"active","name":"absolute configuration","description":"The three-dimensional stereochemical arrangement of a chiral or polar structure.","types":["stereochemical property"],"aliases":[],"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/concepts/co_2379559d7439f07c9e139245c56e1796"},{"public_id":"co_2ccc1ee9e6b17cbfb0a38a30b3602c3f","status":"active","name":"assignment probability","description":"The probability that an absolute-configuration assignment is correct or incorrect as assessed by the chosen index.","types":["probability"],"aliases":[],"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/concepts/co_2ccc1ee9e6b17cbfb0a38a30b3602c3f"},{"public_id":"co_605ba12044ebb3f811d7048134debd08","status":"active","name":"statistically significant reduction in α","description":"A decrease in the probability of making a wrong assignment that is large enough to be statistically significant.","types":["statistical criterion"],"aliases":[],"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/concepts/co_605ba12044ebb3f811d7048134debd08"},{"public_id":"co_7aaa20df7e479f1557f2cf725a14f9cc","status":"active","name":"standard deviation of η","description":"The estimated uncertainty associated with the refined chirality/polarity parameter η.","types":["uncertainty measure"],"aliases":[],"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/concepts/co_7aaa20df7e479f1557f2cf725a14f9cc"},{"public_id":"co_b7959a843004df5e91515f3d7c273cd0","status":"active","name":"α","description":"The probability of making a wrong assignment in the absolute-configuration problem.","types":["error probability"],"aliases":["alpha"],"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/concepts/co_b7959a843004df5e91515f3d7c273cd0"},{"public_id":"co_bba0dceadc3e9638e85c3fd8a6c53dff","status":"active","name":"wrong assignment","description":"An incorrect assignment of absolute configuration.","types":["error"],"aliases":[],"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/concepts/co_bba0dceadc3e9638e85c3fd8a6c53dff"},{"public_id":"co_cb2832cf05b2c3f2ad21e29992ad60d3","status":"active","name":"f0j + f'j + iηf''j","description":"A scattering-factor expression used to model anomalous scatterers in a crystal.","types":["formula"],"aliases":[],"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/concepts/co_cb2832cf05b2c3f2ad21e29992ad60d3"},{"public_id":"co_ee685d1c1839d20ba7ac0f7d50339470","status":"active","name":"R-factor ratio test","description":"A statistical ratio test used to assess evidence for assigning absolute configuration.","types":["statistical test"],"aliases":["R-factor ratio","R"],"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/concepts/co_ee685d1c1839d20ba7ac0f7d50339470"},{"public_id":"co_f9a210eda83bb1c744e4bbc3d54b1d1f","status":"active","name":"anomalous scatterers","description":"Atoms in a crystal whose scattering includes anomalous components.","types":["crystallographic component"],"aliases":[],"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/concepts/co_f9a210eda83bb1c744e4bbc3d54b1d1f"}],"external_ids":{"DOI":"10.1107/S0567739481001629","ArXiv":null,"PubMed":null,"PubMedCentral":null,"MAG":1974864349,"DBLP":null,"ACL":null},"open_access":{"is_open_access":false,"pdf_url":null,"landing_url":"https://sah.borca.ai/papers/94126379","source":null,"pdf_url_source":null,"license":null,"reason":"pdf_url_not_indexed"},"reference_availability":{"status":"available","references_indexed":true,"full_text_available":false,"full_text_source":null,"count_basis":"semantic_scholar_metadata","extraction_status":"not_applicable","reason":null},"source":{"provider":"episteme2","base_corpus":"semantic_scholar_dump","freshness_mode":"unknown","basis":["semantic_scholar_metadata","postgres_metadata"],"limits":["paper metadata is based on indexed upstream scholarly datasets","claims and concepts are available only for extracted papers","absence of claims or concepts means no extracted graph data is available in this response"],"status":"available","degraded":false,"degraded_reasons":[],"diagnostics":{"status":"available","degraded":false,"degraded_reasons":[],"metadata_status":"available","graph_status":"available","abstract_status":"available"},"source_flags":1},"paper_id":631022,"paper_uid":"0ccac077-ddb6-4a91-be65-7f43deed2d82","canonical_identity":{"paper_id":631022,"paper_uid":"0ccac077-ddb6-4a91-be65-7f43deed2d82","identity_status":"available","lookup_basis":"semantic_scholar_external_id","compatibility_path":"corpus_id"},"url":"https://sah.borca.ai/papers/94126379"}