<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//NLM//DTD JATS (Z39.96) Journal Publishing DTD v1.3 20210610//EN" "JATS-journalpublishing1-3.dtd">
<article article-type="research-article" dtd-version="1.3" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xml:lang="en"><front><journal-meta><journal-id journal-id-type="publisher-id">sechenov</journal-id><journal-title-group><journal-title xml:lang="en">Sechenov Medical Journal</journal-title><trans-title-group xml:lang="ru"><trans-title>Сеченовский вестник</trans-title></trans-title-group></journal-title-group><issn pub-type="ppub">2218-7332</issn><issn pub-type="epub">2658-3348</issn><publisher><publisher-name>Сеченовский Университет</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.47093/2218-7332.2024.15.2.4-12</article-id><article-id custom-type="elpub" pub-id-type="custom">sechenov-1100</article-id><article-categories><subj-group subj-group-type="heading"><subject>Research Article</subject></subj-group><subj-group subj-group-type="section-heading" xml:lang="en"><subject>BIOMEDICAL STATISTICS TUTORIAL</subject></subj-group><subj-group subj-group-type="section-heading" xml:lang="ru"><subject>РУКОВОДСТВО ПО БИОМЕДИЦИНСКОЙ СТАТИСТИКЕ</subject></subj-group></article-categories><title-group><article-title>Basic aspects of meta-analysis. Part 2</article-title><trans-title-group xml:lang="ru"><trans-title>Базовые аспекты мета-анализа. Часть 2</trans-title></trans-title-group></title-group><contrib-group><contrib contrib-type="author" corresp="yes"><contrib-id contrib-id-type="orcid">https://orcid.org/0000-0002-0621-7054</contrib-id><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Тао</surname><given-names>Е. А.</given-names></name><name name-style="western" xml:lang="en"><surname>Tao</surname><given-names>E. A.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Тао Екатерина Александровна, канд. мед. наук, ассистент кафедры внутренних, профессиональных болезней и ревматологии</p><p>ул. Трубецкая, д. 8, стр. 2, г. Москва, 119048</p></bio><bio xml:lang="en"><p>Ekaterina A. Tao, Cand. of Sci. (Medicine), Assistant Professor, Department of Internal, Occupational Diseases and Rheumatology</p><p>8/2, Trubetskaya str., Moscow, 119048</p></bio><email xlink:type="simple">tao_e_a@staff.sechenov.ru</email><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><contrib-id contrib-id-type="orcid">https://orcid.org/0000-0002-1210-2528</contrib-id><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Надинская</surname><given-names>М. Ю.</given-names></name><name name-style="western" xml:lang="en"><surname>Nadinskaia</surname><given-names>M. Yu.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Надинская Мария Юрьевна, канд. мед. наук, доцент кафедры пропедевтики внутренних болезней, гастроэнтерологии и гепатологии</p><p>ул. Трубецкая, д. 8, стр. 2, г. Москва, 119048</p></bio><bio xml:lang="en"><p>Maria Yu. Nadinskaia, Cand. of Sci. (Medicine), Associate Professor, Department of Propaedeutics of Internal Diseases, Gastroenterology and Hepatology</p><p>8/2, Trubetskaya str., Moscow, 119048</p></bio><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><contrib-id contrib-id-type="orcid">https://orcid.org/0000-0002-2224-0019</contrib-id><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Суворов</surname><given-names>А. Ю.</given-names></name><name name-style="western" xml:lang="en"><surname>Suvorov</surname><given-names>A. Yu.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Суворов Александр Юрьевич, канд. мед. наук, главный статистик отдела исследовательских сервисов Управления по научному развитию и клиническим исследованиям</p><p>ул. Трубецкая, д. 8, стр. 2, г. Москва, 119048</p></bio><bio xml:lang="en"><p>Alexander Yu. Suvorov, Cand. of Sci. (Medicine), Chief Statistician, Department of Research Services, Office of Scientific Development and Clinical Research</p><p>8/2, Trubetskaya str., Moscow, 119048</p></bio><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><contrib-id contrib-id-type="orcid">https://orcid.org/0000-0002-3989-2590</contrib-id><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Буланов</surname><given-names>Н. М.</given-names></name><name name-style="western" xml:lang="en"><surname>Bulanov</surname><given-names>N. M.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Буланов Николай Михайлович, канд. мед. наук, доцент кафедры внутренних, профессиональных болезней и ревматологии</p><p>ул. Трубецкая, д. 8, стр. 2, г. Москва, 119048</p></bio><bio xml:lang="en"><p>Nikolay M. Bulanov, Cand. of Sci. (Medicine), Associate Professor, Department of Internal, Occupational Diseases and Rheumatology</p><p>8/2, Trubetskaya str., Moscow, 119048</p></bio><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><contrib-id contrib-id-type="orcid">https://orcid.org/0000-0002-8785-7968</contrib-id><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Шоломова</surname><given-names>В. И.</given-names></name><name name-style="western" xml:lang="en"><surname>Sholomova</surname><given-names>V. I.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Шоломова Виктория Игоревна, канд. мед. наук, доцент кафедры внутренних, профессиональных болезней и ревматологии</p><p>ул. Трубецкая, д. 8, стр. 2, г. Москва, 119048</p></bio><bio xml:lang="en"><p>Victoria I. Sholomova, Cand. of Sci. (Medicine), Associate Professor, Department of Internal, Occupational Diseases and Rheumatology</p><p>8/2, Trubetskaya str., Moscow, 119048</p></bio><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><contrib-id contrib-id-type="orcid">https://orcid.org/0000-0003-4366-2832</contrib-id><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Потапов</surname><given-names>П. П.</given-names></name><name name-style="western" xml:lang="en"><surname>Potapov</surname><given-names>P. P.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Потапов Павел Петрович, ассистент кафедры внутренних, профессиональных болезней и ревматологии</p><p>ул. Трубецкая, д. 8, стр. 2, г. Москва, 119048</p></bio><bio xml:lang="en"><p>Pavel P. Potapov, Assistant Professor, Department of Internal, Occupational Diseases and Rheumatology</p><p>8/2, Trubetskaya str., Moscow, 119048</p></bio><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><contrib-id contrib-id-type="orcid">https://orcid.org/0000-0003-4369-173X</contrib-id><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Тараткин</surname><given-names>М. С.</given-names></name><name name-style="western" xml:lang="en"><surname>Taratkin</surname><given-names>M. S.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Тараткин Марк Сергеевич, начальник отдела развития молодежной науки Управления по научному развитию и клиническим исследованиям</p><p>ул. Трубецкая, д. 8, стр. 2, г. Москва, 119048</p></bio><bio xml:lang="en"><p>Mark S. Taratkin, Head of Department of Youth Science Development, Office of Scientific Development and Clinical Research</p><p>8/2, Trubetskaya str., Moscow, 119048</p></bio><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><contrib-id contrib-id-type="orcid">https://orcid.org/0000-0003-0023-2701</contrib-id><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Бровко</surname><given-names>М. Ю.</given-names></name><name name-style="western" xml:lang="en"><surname>Brovko</surname><given-names>M. Yu.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Бровко Михаил Юрьевич, д-р. мед. наук, профессор кафедры внутренних, профессиональных болезней и ревматологии; проректор по международной деятельности</p><p>ул. Трубецкая, д. 8, стр. 2, г. Москва, 119048</p></bio><bio xml:lang="en"><p>Mikhail Yu. Brovko, Doctor of Sci. (Medicine), Professor, Department of Internal, Occupational Diseases and Rheumatology; Vice-rector for International Affairs</p><p>8/2, Trubetskaya str., Moscow, 119048</p></bio><xref ref-type="aff" rid="aff-1"/></contrib></contrib-group><aff-alternatives id="aff-1"><aff xml:lang="ru"><institution>ФГАОУ ВО «Первый Московский государственный медицинский университет им. И.М. Сеченова» Минздрава России (Сеченовский Университет)</institution><country>Россия</country></aff><aff xml:lang="en"><institution>Sechenov First Moscow State Medical University (Sechenov University)</institution><country>Russian Federation</country></aff></aff-alternatives><pub-date pub-type="collection"><year>2024</year></pub-date><pub-date pub-type="epub"><day>31</day><month>07</month><year>2024</year></pub-date><volume>15</volume><issue>2</issue><fpage>4</fpage><lpage>12</lpage><permissions><copyright-statement>Copyright &amp;#x00A9; Tao E.A., Nadinskaia M.Y., Suvorov A.Y., Bulanov N.M., Sholomova V.I., Potapov P.P., Taratkin M.S., Brovko M.Y., 2024</copyright-statement><copyright-year>2024</copyright-year><copyright-holder xml:lang="ru">Тао Е.А., Надинская М.Ю., Суворов А.Ю., Буланов Н.М., Шоломова В.И., Потапов П.П., Тараткин М.С., Бровко М.Ю.</copyright-holder><copyright-holder xml:lang="en">Tao E.A., Nadinskaia M.Y., Suvorov A.Y., Bulanov N.M., Sholomova V.I., Potapov P.P., Taratkin M.S., Brovko M.Y.</copyright-holder><license xml:lang="ru" license-type="creative-commons-attribution" xlink:href="https://creativecommons.org/licenses/by/4.0/" xlink:type="simple"><license-p>Данная работа распространяется под лицензией Creative Commons Attribution 4.0.</license-p></license><license xml:lang="en" license-type="creative-commons-attribution" xlink:href="https://creativecommons.org/licenses/by/4.0/" xlink:type="simple"><license-p>This work is licensed under a Creative Commons Attribution 4.0 License.</license-p></license></permissions><self-uri xlink:href="https://www.sechenovmedj.com/jour/article/view/1100">https://www.sechenovmedj.com/jour/article/view/1100</self-uri><abstract><p>Meta-analysis combines the results of several scientific studies to obtain a summary quantitative estimation of effect size in order to compare the results of several studies and to identify patterns among them and possible sources of biases. Since the research teams, patients, research protocol, clinical guidelines and time intervals are often different between original scientific studies all these sources of difference can influence the results of each study, causing statistical heterogeneity. Meta-analyses are the highest level of credibility within evidence-based medicine, as they allow us to take into account the influence of many confounding factors and publication biases on the true effect size. Understanding the possible sources of erroneous conclusions in papers will allow researchers to analyze the results of such studies correctly and properly plan their own experiments. In this article the reader will be introduced to methods for identifying and quantifying hidden heterogeneity, such as subgroup analysis and meta-regression. In addition, the reader will learn how to calculate effect size in studies, estimate publication bias mathematically and graphically, and incorporate this estimate into the overall average effect size estimate in meta-analyses.</p></abstract><trans-abstract xml:lang="ru"><p>Мета-анализ объединяет результаты нескольких научных исследований для получения обобщенной количественной оценки величины эффекта, для сравнения результатов нескольких исследований, выявления в них закономерностей и возможных источников разногласий. Поскольку оригинальные научные исследования проводятся разными коллективами авторов, с разными пациентами, в разные временные промежутки, по разным протоколам и клиническим рекомендациям, все перечисленные факторы могут оказывать влияние на результаты отдельно взятого исследования, обусловливая статистическую гетерогенность. Мета- анализы занимают высшую степень достоверности в концепции доказательной медицины, так как позволяют учитывать влияние множества вмешивающихся факторов и публикационных смещений на истинный размер эффекта. Понимание возможных источников ошибочных заключений в исследованиях позволит научным сотрудникам критически относиться к интерпретации результатов и корректно планировать собственные эксперименты. В настоящей статье читатель познакомится с методами выявления и количественной оценки скрытой гетерогенности, такими как анализ подгрупп и метарегрессионный анализ. Кроме того, читатель научится производить расчет размера эффекта в исследованиях, математически и графически оценивать публикационные смещения, а также учитывать эту оценку при проведении мета-анализа в общей усредненной оценке размера эффекта.</p></trans-abstract><kwd-group xml:lang="ru"><kwd>размер эффекта</kwd><kwd>разница средних</kwd><kwd>анализ подгрупп</kwd><kwd>метарегрессионный анализ</kwd><kwd>гетерогенность</kwd><kwd>публикационное смещение</kwd></kwd-group><kwd-group xml:lang="en"><kwd>effect size</kwd><kwd>mean difference</kwd><kwd>subgroup analysis</kwd><kwd>meta-regression analysis</kwd><kwd>heterogeneity</kwd><kwd>publication bias</kwd></kwd-group><funding-group><funding-statement xml:lang="ru">Статья подготовлена при поддержке программы стратегического академического лидерства «Приоритет-2030» ФГАОУ ВО «Первый МГМУ им. И.М. Сеченова» Минздрава России (Сеченовский Университет).</funding-statement><funding-statement xml:lang="en">. This article was supported by the Academic leadership program Priority 2030 proposed by Sechenov First Moscow State Medical University (Sechenov University)</funding-statement></funding-group></article-meta></front><back><ref-list><title>References</title><ref id="cit1"><label>1</label><citation-alternatives><mixed-citation xml:lang="ru">Suvorov A.Y., Latushkina I.V., Gulyaeva K.А., et al. Basic aspects of meta-analysis. Part 1. Sechenov Medical Journal. 2023; 14(1): 4–14. https://doi.org/10.47093/2218-7332.2023.14.1.4-14</mixed-citation><mixed-citation xml:lang="en">Suvorov A.Y., Latushkina I.V., Gulyaeva K.А., et al. Basic aspects of meta-analysis. Part 1. Sechenov Medical Journal. 2023; 14(1): 4–14. https://doi.org/10.47093/2218-7332.2023.14.1.4-14</mixed-citation></citation-alternatives></ref><ref id="cit2"><label>2</label><citation-alternatives><mixed-citation xml:lang="ru">Borenstein M., Higgins J.P.T. Meta-Analysis and Subgroups. Prev Sci. 2013 Apr; 14(2): 134–143. https://doi.org/10.1007/s11121013-0377-7. PMID: 23479191</mixed-citation><mixed-citation xml:lang="en">Borenstein M., Higgins J.P.T. Meta-Analysis and Subgroups. Prev Sci. 2013 Apr; 14(2): 134–143. https://doi.org/10.1007/s11121013-0377-7. PMID: 23479191</mixed-citation></citation-alternatives></ref><ref id="cit3"><label>3</label><citation-alternatives><mixed-citation xml:lang="ru">Berkey C.S., Hoaglin D.C., Mosteller F., Colditz G.A. A randomeffects regression model for meta-analysis. Stat Med. 1995 Feb 28; 14(4): 395–411. https://doi.org/10.1002/sim.4780140406. PMID: 7746979</mixed-citation><mixed-citation xml:lang="en">Berkey C.S., Hoaglin D.C., Mosteller F., Colditz G.A. A randomeffects regression model for meta-analysis. Stat Med. 1995 Feb 28; 14(4): 395–411. https://doi.org/10.1002/sim.4780140406. PMID: 7746979</mixed-citation></citation-alternatives></ref><ref id="cit4"><label>4</label><citation-alternatives><mixed-citation xml:lang="ru">Hedges L.V. Modeling publication selection effects in metaanalysis. J Phys A Math Theor. 1992; 7(2): 246–255. https://doi.org/10.1088/1751-8113/44/8/085201</mixed-citation><mixed-citation xml:lang="en">Hedges L.V. Modeling publication selection effects in metaanalysis. J Phys A Math Theor. 1992; 7(2): 246–255. https://doi.org/10.1088/1751-8113/44/8/085201</mixed-citation></citation-alternatives></ref><ref id="cit5"><label>5</label><citation-alternatives><mixed-citation xml:lang="ru">Dear K.B.G., Begg C.B. An approach for assessing publication bias prior to performing a meta-analysis. Stat Sci. 1992; 7(2): 237–245. https://doi.org/10.1214/ss/1177011363</mixed-citation><mixed-citation xml:lang="en">Dear K.B.G., Begg C.B. An approach for assessing publication bias prior to performing a meta-analysis. Stat Sci. 1992; 7(2): 237–245. https://doi.org/10.1214/ss/1177011363</mixed-citation></citation-alternatives></ref><ref id="cit6"><label>6</label><citation-alternatives><mixed-citation xml:lang="ru">Sutton A.J., Song F., Gilbody S.M., Abrams K.R. Modelling publication bias in meta-analysis: a review. Stat Methods Med Res. 2000 Oct; 9(5): 421–445. https://doi.org/10.1177/096228020000900503. PMID: 11191259</mixed-citation><mixed-citation xml:lang="en">Sutton A.J., Song F., Gilbody S.M., Abrams K.R. Modelling publication bias in meta-analysis: a review. Stat Methods Med Res. 2000 Oct; 9(5): 421–445. https://doi.org/10.1177/096228020000900503. PMID: 11191259</mixed-citation></citation-alternatives></ref><ref id="cit7"><label>7</label><citation-alternatives><mixed-citation xml:lang="ru">Sterne J.A.C., Egger M. Funnel plots for detecting bias in meta-analysis: guidelines on choice of axis. J Clin Epidemiol. 2001 Oct; 54(10): 1046–1055. https://doi.org/10.1016/S08954356(01)00377-8. PMID: 11576817</mixed-citation><mixed-citation xml:lang="en">Sterne J.A.C., Egger M. Funnel plots for detecting bias in meta-analysis: guidelines on choice of axis. J Clin Epidemiol. 2001 Oct; 54(10): 1046–1055. https://doi.org/10.1016/S08954356(01)00377-8. PMID: 11576817</mixed-citation></citation-alternatives></ref><ref id="cit8"><label>8</label><citation-alternatives><mixed-citation xml:lang="ru">Egger M., Smith G.D., Schneider M., Minder C. Bias in metaanalysis detected by a simple, graphical test. BMJ. 1997 Sep 13; 315(7109): 629–634. https://doi.org/10.1136/bmj.315.7109.629. PMID: 9310563; PMCID: PMC2127453</mixed-citation><mixed-citation xml:lang="en">Egger M., Smith G.D., Schneider M., Minder C. Bias in metaanalysis detected by a simple, graphical test. BMJ. 1997 Sep 13; 315(7109): 629–634. https://doi.org/10.1136/bmj.315.7109.629. PMID: 9310563; PMCID: PMC2127453</mixed-citation></citation-alternatives></ref><ref id="cit9"><label>9</label><citation-alternatives><mixed-citation xml:lang="ru">Begg C.B., Mazumdar M. Operating characteristics of a rank correlation test for publication bias. Biometrics. 1994 Dec; 50(4): 1088–1101. https://doi.org/10.2307/2533446. PMID: 7786990</mixed-citation><mixed-citation xml:lang="en">Begg C.B., Mazumdar M. Operating characteristics of a rank correlation test for publication bias. Biometrics. 1994 Dec; 50(4): 1088–1101. https://doi.org/10.2307/2533446. PMID: 7786990</mixed-citation></citation-alternatives></ref><ref id="cit10"><label>10</label><citation-alternatives><mixed-citation xml:lang="ru">Harbord R.M., Egger M., Sterne J.A.C. A modifi ed test for smallstudy effects in meta-analyses of controlled trials with binary endpoints. Stat Med. 2006 Oct 30; 25(20): 3443–3457. https://doi.org/10.1002/sim.2380. PMID: 16345038</mixed-citation><mixed-citation xml:lang="en">Harbord R.M., Egger M., Sterne J.A.C. A modifi ed test for smallstudy effects in meta-analyses of controlled trials with binary endpoints. Stat Med. 2006 Oct 30; 25(20): 3443–3457. https://doi.org/10.1002/sim.2380. PMID: 16345038</mixed-citation></citation-alternatives></ref><ref id="cit11"><label>11</label><citation-alternatives><mixed-citation xml:lang="ru">Macaskill P., Walter S.D., Irwig L. A comparison of methods to detect publication bias in meta-analysis. Stat Med. 2001 Feb 28; 20(4): 641–654. https://doi.org/10.1002/sim.698. PMID: 11223905.</mixed-citation><mixed-citation xml:lang="en">Macaskill P., Walter S.D., Irwig L. A comparison of methods to detect publication bias in meta-analysis. Stat Med. 2001 Feb 28; 20(4): 641–654. https://doi.org/10.1002/sim.698. PMID: 11223905.</mixed-citation></citation-alternatives></ref><ref id="cit12"><label>12</label><citation-alternatives><mixed-citation xml:lang="ru">Lin L., Chu H. Quantifying publication bias in meta-analysis. Biometrics. 2018 Sep; 74(3): 785–794. https://doi.org/10.1111/biom.12817. Epub 2017 Nov 15. PMID: 29141096; PMCID: PMC5953768</mixed-citation><mixed-citation xml:lang="en">Lin L., Chu H. Quantifying publication bias in meta-analysis. Biometrics. 2018 Sep; 74(3): 785–794. https://doi.org/10.1111/biom.12817. Epub 2017 Nov 15. PMID: 29141096; PMCID: PMC5953768</mixed-citation></citation-alternatives></ref><ref id="cit13"><label>13</label><citation-alternatives><mixed-citation xml:lang="ru">Bakbergenuly I., Hoaglin D.C., Kulinskaya E. Estimation in meta-analyses of mean difference and standardized mean difference. Stat Med. 2020 Jan 30; 39(2): 171–191. https://doi.org/10.1002/sim.8422. Epub 2019 Nov 11. PMID: 31709582; PMCID: PMC6916299</mixed-citation><mixed-citation xml:lang="en">Bakbergenuly I., Hoaglin D.C., Kulinskaya E. Estimation in meta-analyses of mean difference and standardized mean difference. Stat Med. 2020 Jan 30; 39(2): 171–191. https://doi.org/10.1002/sim.8422. Epub 2019 Nov 11. PMID: 31709582; PMCID: PMC6916299</mixed-citation></citation-alternatives></ref><ref id="cit14"><label>14</label><citation-alternatives><mixed-citation xml:lang="ru">Cohen J. Statistical Power Analysis for the Behavioral Sciences. Second Edition. New Jersey: Lawrence Erlbaum Associates; 1988. 579 p. ISBN 0-8058-0283-5</mixed-citation><mixed-citation xml:lang="en">Cohen J. Statistical Power Analysis for the Behavioral Sciences. Second Edition. New Jersey: Lawrence Erlbaum Associates; 1988. 579 p. ISBN 0-8058-0283-5</mixed-citation></citation-alternatives></ref><ref id="cit15"><label>15</label><citation-alternatives><mixed-citation xml:lang="ru">Friedrich J.O., Adhikari N.K.J., Beyene J. The ratio of means method as an alternative to mean differences for analyzing continuous outcome variables in meta-analysis: A simulation study. BMC Med Res Methodol. 2008; 8(1): 32. https://doi.org/10.1186/1471-2288-8-32</mixed-citation><mixed-citation xml:lang="en">Friedrich J.O., Adhikari N.K.J., Beyene J. The ratio of means method as an alternative to mean differences for analyzing continuous outcome variables in meta-analysis: A simulation study. BMC Med Res Methodol. 2008; 8(1): 32. https://doi.org/10.1186/1471-2288-8-32</mixed-citation></citation-alternatives></ref></ref-list><fn-group><fn fn-type="conflict"><p>The authors declare that there are no conflicts of interest present.</p></fn></fn-group></back></article>
