Media, social scientists and public health researchers often present comparisons across countries, and policy makers use such comparisons to take evidence-based action. For a meaningful comparison among countries, one often needs to normalize the measure for differences in population size. To address this issue, the first choice is usually to calculate per capita ratios. Such ratios, however, normalize the measure for differences in population size directly only under the highly restrictive assumption of a proportional increase of the measure with population size. Violation of this assumption frequently leads to misleading conclusions. We compare per capita ratios with an approach based on regression, a widely used statistical procedure that eliminates many of the problems with ratios and allows for straightforward data interpretation. It turns out that the per capita measures in three global datasets (gross domestic product, COVID-19-related mortality and CO2 production) systematically overestimate values in countries with small populations, while countries with large populations tend to have misleadingly low per capita ratios owing to the large denominators. Unfortunately, despite their biases, comparisons based on per capita ratios are still ubiquitous, and they are used for influential recommendations by various global institutions. Their continued use can cause significant damage when employed as evidence for policy actions and should therefore be replaced by a more scientifically substantiated and informative method, such as a regression-based approach.

Department of Ecology Faculty of Science Charles University Viničná 7 Prague 128 00 Czech Republic

Department of Zoology Faculty of Science Charles University Viničná 7 Prague 128 00 Czech Republic

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IDNES.cz, ČTK . 2020. Globální spotřeba piva v loňském roce vzrostla, jedničkou zůstává Česko. See https://www.idnes.cz/ekonomika/zahranicni/globalni-spotreba-pivo-narust-ceska-republika-prumerna-spotreba-asie-afrika.A201223_153315_eko-zahranicni_misl (accessed 17 January 2024).

Novinky, ČTK, Aš . 2021. Nová statistika: Česko má nejvíc obětí koronaviru na obyvatele na světě. See https://www.novinky.cz/clanek/koronavirus-nova-statistika-cesko-ma-nejvic-obeti-koronaviru-na-obyvatele-na-svete-40356693 (accessed 17 January 2024).

ČTK . 2023. Životní úroveň v Česku se mírně snížila oproti Evropské unii. Před zeměmi Visegrádu ale vede. See https://www.irozhlas.cz/ekonomika/zivotni-uroven-cesko-srovnani-eu-statisticka-rocenka_2311271150_kac (accessed 17 January 2024).

Saslow E. 2018. Gun violence’s distant echo. See https://www.washingtonpost.com/news/national/wp/2018/05/18/feature/a-teenager-wanted-to-talk-about-gun-control-would-anyone-in-her-town-listen/ (accessed 17 January 2024).

Shryock T, Payerchin R. 2023. Doctor salaries under fire after Washington Post report. See https://www.medicaleconomics.com/view/doctor-salaries-under-fire-after-washington-post-report (accessed 17 January 2024).

Shank M. 2024. Stop the finger-pointing, democrats. You’re in the grip of big oil. See https://www.newsweek.com/stop-finger-pointing-democrats-youre-grip-big-oil-opinion-1859676 (accessed 17 January 2024).

Black RE, Morris SS, Bryce J. 2003. Where and why are 10 million children dying every year? Lancet 361 , 2226–2234. (10.1016/S0140-6736(03)13779-8) PubMed DOI

Anell A, Willis M. 2000. International comparison of health care systems using resource profiles. Bull. World Health Org. 78 , 770–778. (10.1590/S0042-96862000000600009) PubMed DOI PMC

Ridley M, Rao G, Schilbach F, Patel V. 2020. Poverty, depression, and anxiety: causal evidence and mechanisms. Science 370 , eaay0214. (10.1126/science.aay0214) PubMed DOI

Silva WTAF. 2020. Per capita death and infection rates should be avoided in international comparisons. Public Health 186 , 18–19. (10.1016/j.puhe.2020.06.038) PubMed DOI PMC

Sokal R, Rohlf F. 1969. Biometry: the principles and practices of statistics in biological research. San Francisco, CA: Freeman.

Lolli L, Batterham AM, Kratochvíl L, Flegr J, Weston KL, Atkinson G. 2017. A comprehensive allometric analysis of 2nd digit length to 4th digit length in humans. Proc. Biol. Sci. B 284 , 20170356. (10.1098/rspb.2017.0356) PubMed DOI PMC

Kratochvíl L, Rovatsos M. 2022. Ratios of non- synonymous to synonymous mutations can be misleading for detecting selection. Curr. Biol. 32 , R28–R30. (10.1016/j.cub.2021.11.066) PubMed DOI

Isles PDF. 2020. The misuse of ratios in ecological stoichiometry. Ecology 101 , 1–7. (10.1002/ecy.3153) PubMed DOI

Li X, Lin B. 2013. Global convergence in per capita CO2 emissions. Renew. Sustain. Energy Rev. 24 , 357–363. (10.1016/j.rser.2013.03.048) DOI

WHO . 2019. Global spending on health: a world in transition 2019. See https://www.who.int/health_financing/documents/health-expenditure-report-2019.pdf?ua=1

Stiglitz JE, Sen A, Fitoussi JP. 2009. Report by the commission on the measurement of economic performance and social progress.

Costanza R, Hart M, Posner S, Talberth J. 2009. Beyond GDP: the need for new measures of progress beyond GDP. Pardee Pap 4 , 1–47.

Corrao G, Rea F, Blangiardo GC. 2021. Lessons from COVID-19 mortality data across countries. J. Hypertens. 39 , 856–860. (10.1097/HJH.0000000000002833) PubMed DOI PMC

Middelburg RA, Rosendaal FR. 2020. COVID-19: how to make between-country comparisons. Int. J. Infect. Dis. 96 , 477–481. (10.1016/j.ijid.2020.05.066) PubMed DOI PMC

WHO COVID 19. 2024. See https://covid19.who.int/ (accessed 18 January 2024).

World Bank. 2022. World Development Report 2022: finance for an equitable recovery. Washington, DC.: World Bank Publications.

Giannetti BF, Agostinho F, Almeida CMVB, Huisingh D. 2015. A review of limitations of GDP and alternative indices to monitor human wellbeing and to manage eco-system functionality. J. Clean. Prod. 87 , 11–25. (10.1016/j.jclepro.2014.10.051) DOI

Ranzani OT, Bastos LSL, Gelli JGM, Marchesi JF, Baião F, Hamacher S, Bozza FA. 2021. Characterisation of the first 250 000 hospital admissions for COVID-19 in Brazil: a retrospective analysis of nationwide data. Lancet Respir. Med. 9 , 407–418. (10.1016/S2213-2600(20)30560-9) PubMed DOI PMC

Jin J, Agarwala N, Kundu P, Harvey B, Zhang Y, Wallace E, Chatterjee N. 2021. Individual and community-level risk for COVID-19 mortality in the United States. Nat. Med. 27 , 264–269. (10.1038/s41591-020-01191-8) PubMed DOI

Sempé L, Lloyd-Sherlock P, Martínez R, Ebrahim S, McKee M, Acosta E. 2021. Estimation of all-cause excess mortality by age-specific mortality patterns for countries with incomplete vital statistics: a population-based study of the case of Peru during the first wave of the COVID-19 pandemic. Lancet Reg. Heal. - Am. 2 , 100039. (10.1016/j.lana.2021.100039) PubMed DOI PMC

Ranta E, Laurila A, Elmberg J. 1994. Reinventing the wheel: analysis of sexual dimorphism in body size. Oikos 70 , 313. (10.2307/3545768) DOI

Atchley WR, Gaskins CT, Anderson D. 1976. Statistical properties of ratios. I. Empirical results. Syst. Zool. 25 , 137–148. (10.2307/2412740) DOI

Curran-Everett D. 2013. Explorations in statistics: the analysis of ratios and normalized data. Am. J. Physiol. - Adv. Physiol. Educ. 37 , 213–219. (10.1152/advan.00053.2013) PubMed DOI

Jasienski M, Bazzaz FA. 1999. The fallacy of ratios and the testability of models in biology. Oikos 84 , 321–326. (10.2307/3546729) DOI

Sorokowski P, Kowal M. 2024. Relationship between the 2D:4D and prenatal testosterone, adult level testosterone, and testosterone change: meta-analysis of 54 studies. Am. J. Biol. Anthropol. 183 , 20–38. (10.1002/ajpa.24852) PubMed DOI

Kratochvíl L, Flegr J. 2009. Differences in the 2nd to 4th digit length ratio in humans reflect shifts along the common allometric line. Biol. Lett. 5 , 643–646. (10.1098/rsbl.2009.0346) PubMed DOI PMC

Menge DNL, MacPherson AC, Bytnerowicz TA, Quebbeman AW, Schwartz NB, Taylor BN, Wolf AA. 2018. Logarithmic scales in ecological data presentation may cause misinterpretation. Nat. Ecol. Evol. 2 , 1393–1402. (10.1038/s41559-018-0610-7) PubMed DOI

Barton RA, Montgomery SH. 2019. Proportional versus relative size as metrics in human brain evolution. Proc. Acad. Sci. USA 116 , 3–4. (10.1073/pnas.1817200116). PubMed DOI PMC

Field A. 2013. Discovering statistics using IBM SPSS statistics. London, UK: Sage Publications.

International Monetary Fund. Real GDP growth. 2024. See https://www.imf.org/external/datamapper/NGDP_RPCH@WEO/OEMDC/ADVEC/WEOWORLD (accessed 18 January 2024).

Eurostat 2024. See https://ec.europa.eu/eurostat/databrowser/view/sdg_08_10/default/table?lang=en (accessed 18 January 2024).

United Nations Data 2024. See https://data.un.org/Data.aspx?d=SNAAMA&f=grID%3A101%3BcurrID%3AUSD%3BpcFlag%3A1 (accessed 18 January 2024).

Wikipedia 2024. See https://en.wikipedia.org/wiki/Gross_domestic_product (accessed 18 January 2024).

GDP per capita, consumption per capita and price level indices 2023. See https://ec.europa.eu/eurostat/statistics-explained/index.php?title=GDP_per_capita,_consumption_per_capita_and_price_level_indices (accessed 18 January 2024).

The World Bank . 2024. Data from: Data catalog. The World Bank. https://datacatalog.worldbank.org/home

Worldometer . 2024. Data from: COVID-19 coronavirus pandemic. Worldometer. https://www.worldometers.info/coronavirus/#countries

Worldometer . 2016. Data from: CO2 emissions. Worldometer. https://www.worldometers.info/co2-emissions/

Kratochvíl L, Havlíček J. 2024. Data from: The fallacy of global comparisons based on per capita measures. Figshare. (10.6084/m9.figshare.c.7100061) PubMed DOI PMC

The fallacy of global comparisons based on per capita measures

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