# Most-cited Mathematics papers of 2021, with free PDFs

The 25 most-cited Mathematics research papers published in 2021, ranked by citations in OpenAlex, with their original abstracts and free PDFs where available.

1. [The coefficient of determination R-squared is more informative than SMAPE, MAE, MAPE, MSE and RMSE in regression analysis evaluation](https://nerdi.pages.dev/paper/W3182706339) · 5,334 citations
2. [A global panel database of pandemic policies (Oxford COVID-19 Government Response Tracker)](https://nerdi.pages.dev/paper/W3135257712) · 4,636 citations · Free PDF
3. [Sample size determination and power analysis using the G*Power software](https://nerdi.pages.dev/paper/W3183286355) · 2,542 citations
4. [Estimated transmissibility and impact of SARS-CoV-2 lineage B.1.1.7 in England](https://nerdi.pages.dev/paper/W3134208712) · 2,286 citations
5. [Synthetic Difference-in-Differences](https://nerdi.pages.dev/paper/W2952814763) · 1,526 citations · Free PDF
6. [Using Synthetic Controls: Feasibility, Data Requirements, and Methodological Aspects](https://nerdi.pages.dev/paper/W3169407454) · 1,512 citations
7. [Mendelian randomisation for mediation analysis: current methods and challenges for implementation](https://nerdi.pages.dev/paper/W3159102563) · 1,214 citations · Free PDF
8. [SARS-CoV-2 Transmission From People Without COVID-19 Symptoms](https://nerdi.pages.dev/paper/W3118409314) · 1,036 citations
9. [A survey on missing data in machine learning](https://nerdi.pages.dev/paper/W3170657538) · 1,033 citations · Free PDF
10. [Novel coronavirus 2019-nCoV (COVID-19): early estimation of epidemiological parameters and epidemic size estimates](https://nerdi.pages.dev/paper/W3165423827) · 1,003 citations
11. [An introduction to inverse probability of treatment weighting in observational research](https://nerdi.pages.dev/paper/W3205211596) · 955 citations
12. [Interrupted time series analysis using autoregressive integrated moving average (ARIMA) models: a guide for evaluating large-scale health interventions](https://nerdi.pages.dev/paper/W3138970751) · 796 citations · Free PDF
13. [Effectiveness of public health measures in reducing the incidence of covid-19, SARS-CoV-2 transmission, and covid-19 mortality: systematic review and meta-analysis](https://nerdi.pages.dev/paper/W3212693288) · 792 citations · Free PDF
14. [Tracking excess mortality across countries during the COVID-19 pandemic with the World Mortality Dataset](https://nerdi.pages.dev/paper/W3173464765) · 774 citations
15. [Model-informed COVID-19 vaccine prioritization strategies by age and serostatus](https://nerdi.pages.dev/paper/W3123021790) · 745 citations
16. [From Frege to Gödel: a source book in mathematical logic, 1879-1931](https://nerdi.pages.dev/paper/W1607953571) · 738 citations
17. [Guidelines for Designing and Evaluating Feasibility Pilot Studies](https://nerdi.pages.dev/paper/W3215891836) · 712 citations
18. [Covasim: An agent-based model of COVID-19 dynamics and interventions](https://nerdi.pages.dev/paper/W3186633320) · 696 citations · Free PDF
19. [Cobaya: code for Bayesian analysis of hierarchical physical models](https://nerdi.pages.dev/paper/W3021130000) · 693 citations · Free PDF
20. [The Impact of Vaccination on Coronavirus Disease 2019 (COVID-19) Outbreaks in the United States](https://nerdi.pages.dev/paper/W3128361403) · 689 citations
21. [geomorph v4.0 and gmShiny: Enhanced analytics and a new graphical interface for a comprehensive morphometric experience](https://nerdi.pages.dev/paper/W3200034595) · 654 citations
22. [Violating the normality assumption may be the lesser of two evils](https://nerdi.pages.dev/paper/W3158727545) · 649 citations · Free PDF
23. [Mediation, Moderation, and Conditional Process Analysis: Concepts, Computations, and Some Common Confusions](https://nerdi.pages.dev/paper/W3205473651) · 630 citations
24. [Simulation-Based Power Analysis for Factorial Analysis of Variance Designs](https://nerdi.pages.dev/paper/W3138585281) · 609 citations
25. [Reduction in mobility and COVID-19 transmission](https://nerdi.pages.dev/paper/W3121139527) · 598 citations · Free PDF

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