{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,17]],"date-time":"2026-10-17T21:50:16Z","timestamp":1792273816964,"version":"4.4.0"},"reference-count":67,"publisher":"SAGE Publications","issue":"3","license":[{"start":{"date-parts":[[2020,12,3]],"date-time":"2020-12-03T00:00:00Z","timestamp":1606953600000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/journals.sagepub.com\/page\/policies\/text-and-data-mining-license"}],"funder":[{"name":"Pinsent Darwin Fund"},{"DOI":"10.13039\/501100007602","name":"Programme Grants for Applied Research","doi-asserted-by":"publisher","award":["RP-PG-0616-20003"],"award-info":[{"award-number":["RP-PG-0616-20003"]}],"id":[{"id":"10.13039\/501100007602","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100000265","name":"medical research council","doi-asserted-by":"publisher","id":[{"id":"10.13039\/501100000265","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100000272","name":"national institute for health research","doi-asserted-by":"publisher","award":["NIHR200177"],"award-info":[{"award-number":["NIHR200177"]}],"id":[{"id":"10.13039\/501100000272","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["journals.sagepub.com"],"crossmark-restriction":true},"short-container-title":["Assessment"],"published-print":{"date-parts":[[2022,4]]},"abstract":"<jats:p>In psychiatry, severity of mental health conditions and their change over time are usually measured via sum scores of items on psychometric scales. However, inferences from such scores can be biased if psychometric properties such as unidimensionality and temporal measurement invariance for instruments are not met. Here, we aimed to evaluate these properties for common measures of depression (Patient Health Questionnaire\u20139) and anxiety (Generalized Anxiety Disorder Assessment\u20137) in a large clinical sample ( N = 22,362) undergoing psychotherapy. In addition, we tested consistency in dimensionality results across different methods (parallel analysis, factor analysis, explained common variance, the partial credit model, and the Mokken model). Results showed that while both Patient Health Questionnaire\u20139 and Generalized Anxiety Disorder Assessment\u20137 are multidimensional instruments with highly correlated factors, there is justification for sum scores as measures of severity. Temporal measurement invariance across 10 therapy sessions was evaluated. Strict temporal measurement invariance was established in both scales, allowing researchers to compare sum scores as severity measures across time.<\/jats:p>","DOI":"10.1177\/1073191120976863","type":"journal-article","created":{"date-parts":[[2020,12,3]],"date-time":"2020-12-03T06:39:56Z","timestamp":1606977596000},"page":"355-366","update-policy":"https:\/\/doi.org\/10.1177\/sage-journals-update-policy","source":"Crossref","is-referenced-by-count":82,"title":["On Dimensionality, Measurement Invariance, and Suitability of Sum Scores for the PHQ-9 and the GAD-7"],"prefix":"10.1177","volume":"29","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-9693-9930","authenticated-orcid":false,"given":"Jan","family":"Stochl","sequence":"first","affiliation":[{"name":"University of Cambridge, Cambridge, UK"},{"name":"National Institute for Health Research Collaboration for Leadership in Applied Health Research and Care East of England, Cambridge, UK"},{"name":"Charles University, Prague, Czech Republic"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Eiko I.","family":"Fried","sequence":"additional","affiliation":[{"name":"Leiden University, Leiden, Zuid-Holland, Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jessica","family":"Fritz","sequence":"additional","affiliation":[{"name":"University of Cambridge, Cambridge, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8346-7463","authenticated-orcid":false,"given":"Tim J.","family":"Croudace","sequence":"additional","affiliation":[{"name":"University of Dundee, Dundee, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Debra A.","family":"Russo","sequence":"additional","affiliation":[{"name":"University of Cambridge, Cambridge, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Clare","family":"Knight","sequence":"additional","affiliation":[{"name":"University of Cambridge, Cambridge, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Peter B.","family":"Jones","sequence":"additional","affiliation":[{"name":"University of Cambridge, Cambridge, UK"},{"name":"National Institute for Health Research Collaboration for Leadership in Applied Health Research and Care East of England, Cambridge, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jesus","family":"Perez","sequence":"additional","affiliation":[{"name":"University of Cambridge, Cambridge, UK"},{"name":"National Institute for Health Research Collaboration for Leadership in Applied Health Research and Care East of England, Cambridge, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"179","published-online":{"date-parts":[[2020,12,3]]},"reference":[{"key":"bibr1-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1176\/appi.ajp.161.12.2163"},{"key":"bibr2-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1590\/0102-311x00212716"},{"key":"bibr3-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1016\/j.janxdis.2014.06.002"},{"key":"bibr4-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1037\/0033-2909.107.2.238"},{"key":"bibr5-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1007\/s11336-008-9100-1"},{"key":"bibr6-1073191120976863","doi-asserted-by":"publisher","DOI":"10.3399\/bjgp08X263794"},{"key":"bibr7-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1146\/annurev-clinpsy-050817-084833"},{"key":"bibr8-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1016\/j.jpainsymman.2015.12.303"},{"key":"bibr9-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1016\/j.psychres.2012.05.018"},{"key":"bibr10-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1080\/14737175.2017.1307737"},{"key":"bibr11-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1037\/pas0000275"},{"key":"bibr12-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1007\/BF00172565"},{"key":"bibr13-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1007\/978-1-4612-4230-7_5"},{"key":"bibr14-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1371\/journal.pone.0193356"},{"key":"bibr15-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1016\/j.jad.2017.05.020"},{"key":"bibr16-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1136\/jnnp.23.1.56"},{"key":"bibr17-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1111\/j.2044-8260.1967.tb00530.x"},{"key":"bibr18-1073191120976863","doi-asserted-by":"publisher","DOI":"10.3389\/fams.2016.00003"},{"key":"bibr19-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1007\/BF02289447"},{"key":"bibr20-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1080\/10705519909540118"},{"key":"bibr21-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1207\/S15328007SEM0902_5"},{"key":"bibr22-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1016\/j.jpsychores.2012.12.012"},{"key":"bibr23-1073191120976863","doi-asserted-by":"publisher","DOI":"10.3389\/fpsyg.2019.01713"},{"key":"bibr24-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1038\/mp.2012.105"},{"key":"bibr25-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1002\/cpp.1802"},{"key":"bibr26-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1037\/pas0000550"},{"key":"bibr27-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1016\/j.jad.2020.04.015"},{"key":"bibr28-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1016\/j.apmr.2010.04.015"},{"key":"bibr29-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1046\/j.1525-1497.2001.016009606.x"},{"key":"bibr30-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1080\/00273171.2015.1134306"},{"key":"bibr31-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1080\/24750573.2019.1691320"},{"key":"bibr32-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1136\/bmj.l1476"},{"key":"bibr33-1073191120976863","unstructured":"Linacre J. M. (2002). What do infit and outfit, mean-square and standardized mean? Rasch Measurement Transactions, 16(2), 878. https:\/\/www.rasch.org\/rmt\/rmt162f.htm"},{"key":"bibr34-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1037\/h0093565"},{"key":"bibr35-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1097\/MLR.0b013e318160d093"},{"key":"bibr36-1073191120976863","doi-asserted-by":"publisher","DOI":"10.18637\/jss.v020.i09"},{"key":"bibr37-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1503\/cmaj.110829"},{"key":"bibr38-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1186\/s12978-019-0802-x"},{"key":"bibr39-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1007\/BF02296272"},{"key":"bibr40-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1007\/978-1-4757-2691-6_6"},{"key":"bibr41-1073191120976863","volume-title":"Test theory: A unified treatment","author":"McDonald R. P.","year":"1999"},{"key":"bibr42-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1007\/BF02294825"},{"key":"bibr43-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1016\/j.brat.2014.10.001"},{"key":"bibr44-1073191120976863","volume-title":"Statistical approaches to measurement invariance","author":"Millsap R. E.","year":"2011"},{"key":"bibr45-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1515\/9783110813203"},{"key":"bibr46-1073191120976863","unstructured":"Muth\u00e9n B., Asparouhov T. (2013). Mplus language addendum (Version 7.1) [Computer software]. https:\/\/www.statmodel.com\/download\/Version7.1xLanguage.pdf"},{"key":"bibr47-1073191120976863","volume-title":"Mplus user\u2019s guide: Eighth edition","author":"Muth\u00e9n L. K.","year":"1998"},{"key":"bibr48-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1017\/S0033291713001967"},{"key":"bibr49-1073191120976863","unstructured":"NHS Digital. (2020). Psychological therapies: Reports on the use of IAPT services, England October 2019 Final including reports on the IAPT pilots. https:\/\/digital.nhs.uk\/data-and-information\/publications\/statistical\/psychological-therapies-report-on-the-use-of-iapt-services\/october-2019-final-including-reports-on-the-iapt-pilots"},{"key":"bibr50-1073191120976863","doi-asserted-by":"publisher","DOI":"10.18637\/jss.v074.i11"},{"key":"bibr51-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1016\/j.neubiorev.2014.05.010"},{"key":"bibr52-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1080\/00223891.2010.496477"},{"key":"bibr53-1073191120976863","unstructured":"Revelle W. (2018). psych: Procedures for personality and psychological research (Version 1.8.12) [Computer software]. https:\/\/CRAN.R-project.org\/package=psych"},{"key":"bibr54-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1037\/0090-5550.53.2.243"},{"key":"bibr55-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1002\/jclp.20213"},{"key":"bibr56-1073191120976863","doi-asserted-by":"publisher","DOI":"10.4135\/9781412984676"},{"key":"bibr57-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1037\/a0016699"},{"key":"bibr58-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1186\/s12955-015-0244-2"},{"key":"bibr59-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1001\/archinte.166.10.1092"},{"key":"bibr60-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1186\/1471-2288-12-74"},{"key":"bibr61-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1007\/BF02289858"},{"key":"bibr62-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1080\/16506073.2010.550059"},{"key":"bibr63-1073191120976863","doi-asserted-by":"publisher","DOI":"10.18637\/jss.v048.i05"},{"key":"bibr64-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1159\/000443549"},{"key":"bibr65-1073191120976863","unstructured":"Wright B. D., Linacre J. M. (1994). Reasonable mean-square fit values. Rasch Measurement Transactions, 8(3), 370. https:\/\/www.rasch.org\/rmt\/rmt83b.htm"},{"key":"bibr66-1073191120976863","unstructured":"Wright B. D., Masters G. N. (1990). Computation of OUTFIT and INFIT statistics. Rasch Measurement Transactions, 3(4), 84-85. https:\/\/www.rasch.org\/rmt\/rmt34e.htm"},{"key":"bibr67-1073191120976863","doi-asserted-by":"publisher","DOI":"10.1007\/s11336-015-9481-x"}],"container-title":["Assessment"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/journals.sagepub.com\/doi\/pdf\/10.1177\/1073191120976863","content-type":"application\/pdf","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/journals.sagepub.com\/doi\/full-xml\/10.1177\/1073191120976863","content-type":"application\/xml","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/journals.sagepub.com\/doi\/pdf\/10.1177\/1073191120976863","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,4,28]],"date-time":"2026-04-28T12:11:18Z","timestamp":1777378278000},"score":1,"resource":{"primary":{"URL":"https:\/\/journals.sagepub.com\/doi\/10.1177\/1073191120976863"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2020,12,3]]},"references-count":67,"journal-issue":{"issue":"3","published-print":{"date-parts":[[2022,4]]}},"alternative-id":["10.1177\/1073191120976863"],"URL":"https:\/\/doi.org\/10.1177\/1073191120976863","relation":{},"ISSN":["1073-1911","1552-3489"],"issn-type":[{"value":"1073-1911","type":"print"},{"value":"1552-3489","type":"electronic"}],"subject":[],"published":{"date-parts":[[2020,12,3]]}}}