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Calculating the sample size required for developing a clinical prediction model
Open accessAbstract
Clinical prediction models aim to predict outcomes in individuals, to inform diagnosis or prognosis in healthcare. Hundreds of prediction models are published in the medical literature each year, yet many are developed using a dataset that is too small for the total number of participants or outcome events. This leads to inaccurate predictions and consequently incorrect healthcare decisions for some individuals. In this article, the authors provide guidance on how to calculate the sample size required to develop a clinical prediction model.
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“In step three, the sample size needed to reduce model overfitting is calculated, assuming an expected shrinkage rate of 10%, with an expected number of variables P to be included in the final predictive model of 30: S is the expected shrinkage factor, and the noise ratio evaluation index R2cs is 0.3; the calculated sample size is 740 cases.”
From Machine learning-driven prediction model for successful weaning of patients from mechanical ventilation in ICU (2026) · cites this paper as Riley [13]
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In the citing paper
“Genomic and molecular data support integration of tumour biology and genetic risk into decision-making, particularly in precision medicine applications [42].”
From Artificial Intelligence in Clinical Decision-Making: A Comprehensive Review of Diagnostic, Prognostic, and Therapeutic Applications, Validation Gaps, Bias, and Deployment Challenges (2026) · cites this paper as [42]
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“The sample size calculated this way is the minimum for a standard statistical model.”
From Developing clinical prediction models: a step-by-step guide (2024) · cites this paper as [50]
In the citing paper
“Sample size calculations50 indicated a minimum sample of 2082 patients, which is larger than the available sample, raising concerns about possible overfitting issues (step 6).”
From Developing clinical prediction models: a step-by-step guide (2024) · cites this paper as [50]
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Citations
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“We calculated the sample size required for the prediction model using an established rule of thumb that ensures at least 10 events for each predictor parameter [9].”
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“In the multivariate models, this resulted in an excess rate of 10 events per variable, indicating an adequate level of statistical power for the evaluation [23].”
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“In recent years, Riley et al. 28 proposed a widely recognized scienti fi c approach for determining sample sizes in predictive models.”
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“06 [21] and obtaining a required sample size of 220 patients and 4.”
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“At least 1871 patients were required for model development or validation using the R package pmsampsize [24].”
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“…be accurately estimated based on prior similar studies or pilot data, thus enabling the selection of an appropriate sample size calculation formula [10]. a well-calibrated sample size allows the model to learn diverse features and patterns in the data, significantly improving the model’s…”
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“According to a previous study, optimism is acceptable if less than 5% [40].”
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“67 Underrepresentation of groups within a model-building cohort can lead to models that perform poorly in these subpopulations.”
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“Firstly, in the process of evaluating the sample size, we did not choose the empirical-based estimation algorithm of 10-fold EPV but used the calculation method proposed by Richard that guaranteed the expected shrinkage rate and controls the error of individual prediction values [21], which made the calculation of the…”
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“As a rule of thumb, 50 samples or 10 samples per feature (Pedregosa et al., 2011; Riley et al., 2020; Scikit-learn developers, 2023) are minimally needed to fi t predictive or machine learning models.”
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“covering the sample size calculation for developing a clinical prediction model in detail [23], the anticipated R2 of the model could be set as 50% of the maximum R2 when the training dataset included direct measures of the clinical process involved.”
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“These sample sizes are larger than the proposed minima of 3656, when assuming the model will explain 20% of the variability as suggested by Riley et al. [25].”
BackgroundTong, B., Chen, H., Wang, M., Liu, P., Wang, C., Zeng, W., Li, D., & Shang, S. (2024) · BMJ Open · doi:10.1136/bmjopen-2023-076043 · Cited by 18
“27 With six independent variables in this study, and considering the 36.4% prevalence rate of KOA in Chinese individuals over 40 years old, 28 the calculated sample size ranges from 138 to 165 participants.”
MethodInfluentialDong, L., Liu, P., Qi, Z., Lin, J., & Duan, M. (2024) · Heliyon · doi:10.1016/j.heliyon.2024.e29985 · Cited by 19
“The sample size was calculated using the method proposed in the work of Riley et al. [14]: Step 1: Calculate the sample size N1 required to evaluate the overall outcome risk or average outcome value.”
InfluentialBoko, M. F., Khanna, A. K., D’Aragon, F., Spence, J. D., Conen, D., Patel, A., Ayad, S. S., Wijeysundera, D. N., Choinière, M., Sessler, D. I., et al. (2024) · Anesthesiology · doi:10.1097/aln.0000000000005030 · Cited by 22
“Boko et al. We used the approach proposed by Riley et al. 30 to determine the sample size requirement for developing a prediction model to predict chronic postsurgical pain.”
Liu, Y., Feng, H., Du, J., Yang, L., Xue, H., Zhang, J., Liang, Y. Y., & Liu, Y. (2024) · Psychiatry and Clinical Neurosciences · doi:10.1111/pcn.13671 · Cited by 18
“17 In addition, to minimize potential inferential bias, multiple imputations were conducted to assign any missing covariate values using the “ mice ” R package.”
MethodYi, L., Shuai, T., Zhou, J., Cheng, L., Herrera, M., & Tian, X. (2024) · BMC Medical Education · doi:10.1186/s12909-024-06505-9 · Cited by 18
A Review on Predictive Systems and Data Models for COVID-19
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“…designed following the latest guidance 39 : the sample size calculation and recruitment strategy (sampling frame) are based on recent methodological advances, 40 41 and selection of candidate predictors was informed by expert consensus, feasibility and systematic review of the existing evidence.”
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“In addition, the main limitation of such studies is the small sample size, despite being a critical determinant to ensure the robustness and generalizability of the results [27].”
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“Despite this, we suggest as a conservative approach that penalized regression with either modified or bootstrap tuning methods alwaysbeusedinconjunctionwiththerecommendedsamplesize requirements according to the criterion of limiting overfitting and other criteria (Riley et al. 2020).”
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“…minimum sample size for the multivariable logistic regression analysis was determined using two methods: (1) the fi rst method, a classical approach, required a number of events equal to 10 subjects per included variable, and (2) the second method followed the criteria proposed by Riley et al. [13].”
Pu, Z., Huang, H., Li, M., Li, H., Shen, X., Du, L., Wu, Q., Fang, X., Meng, X., Ni, Q., et al. (2025) · NeuroImage · doi:10.1016/j.neuroimage.2025.121130 · Cited by 17
“Another important flaw is that most of these studies only extracted features for which P > 0.05 or > 0.01, which ignored general trends and could lead to overfitting, resulting in an artificial inflated ACC (Ding et al., 2022; Riley et al., 2020).”
InfluentialEnsor, J., Snell, K. I. E., Debray, T. P. A., Lambert, P. C., Look, M. P., Mamas, M. A., Moons, K. G. M., & Riley, R. D. (2021) · Statistics in Medicine · doi:10.1002/sim.8959 · Cited by 17
McDaniel, S., McDaniel, J., Howard, K. M., & Kingsley, K. (2021) · Dentistry Journal · doi:10.3390/dj9060073 · Cited by 17
“In addition, there are limitations associated with the inferences that can be made from this study due to the limitations of this pilot study sample size, a common feature among many clinical and epidemiologic studies that attempt to produce relevant clinical data without significant external funding sources [51,52].”
BackgroundWong, K., Tessema, G. A., Chai, K. E. K., & Pereira, G. F. (2022) · Scientific Reports · doi:10.1038/s41598-022-23782-w · Cited by 17
Tran, N. T. D., Balezeaux, M., Granal, M., Fouque, D. P., Ducher, M., & Fauvel, J. (2022) · Nephrology Dialysis Transplantation · doi:10.1093/ndt/gfac316 · Cited by 18
Li, L., Zhu, Q., Wang, Z., Yun, T., Liu, H., Tang, F., Liu, S., & Zhang, Y. (2023) · Frontiers in Endocrinology · doi:10.3389/fendo.2023.1087994 · Cited by 18
“Based on the 10EPP rule (19), the sample size of our predictor model should be at least 170; our study sample consists of 824 women in the training dataset and 392 women in the validation dataset, and based on the sample size of our study, the power (1 − b) calculation is equal to 1.”
MethodTakeuchi, H., & Kawashima, R. (2023) · Frontiers in Neuroscience · doi:10.3389/fnins.2023.984919 · Cited by 15
“Although, we included a wide range of variables in this study, this study has a rich sample size, which mitigates the problem of overfitting (Riley et al., 2020).”
BackgroundMilders, J., Ramspek, C. L., Janse, R. J., Bos, W. J. W., Rotmans, J. I., Dekker, F. W., & van Diepen, M. (2023) · Journal of the American Society of Nephrology · doi:10.1681/asn.0000000000000285 · Cited by 20
McCurdy, J. D., Munir, J., Parlow, S., Reid, J., Yanofsky, R., Alenezi, T. A., Meserve, J. D., Becker, B., Lahijanian, Z., Eddin, A. H., et al. (2023) · Clinical Gastroenterology and Hepatology · doi:10.1016/j.cgh.2023.12.006 · Cited by 17
Giannella, L., Piva, F., Carpini, G. D., Giuseppe, J. D., Grelloni, C., Giulietti, M., Sopracordevole, F., Giorda, G., Fabro, A. D., Clemente, N., et al. (2023) · Cancers · doi:10.3390/cancers16010172 · Cited by 17
“Based on previous data for prediction models, we considered a minimum of 10 events (EC) for each predictor variable [16].”
MethodEffective sample size: A measure of individual uncertainty in predictions
Thomassen, D., le Cessie, S., van Houwelingen, H. V., & Steyerberg, E. (2023) · Statistics in Medicine · doi:10.1002/sim.10018 · Cited by 22
“21 This would require specification of a minimal n eff for the prediction to be of added value in clinical practice.”
BackgroundSparks, J. A., Dieudé, P., Hoffmann‐Vold, A., Burmester, G. R., Walsh, S. L. F., Kreuter, M., Stock, C., Sambevski, S., Alves, M., & Emery, P. (2024) · BMC Rheumatology · doi:10.1186/s41927-024-00389-4 · Cited by 20
“…based on an assumed number of model parameters of 22 to 24, an assumed prevalence of RA-ILD in the study population (which is enriched for patients with RA-ILD) of 30%, an assumed c-statistic for the model of 0.75, and an assumed shrink-age factor associated with the predictors of 0.9 [52].”
BackgroundInfluentialLin, Z., Yu, L.-Y., Pan, S., Cao, Y., & Lin, P. (2024) · Pain and Therapy · doi:10.1007/s40122-024-00612-7 · Cited by 17
“…the pmsampsize package in R, which implements the specification of the prediction model sam‑ ple size calculation method previously pub‑ lished [34], with the following parameters (type = "b", cstatistic = 0.90, parameters = 8, prevalence = 0.4), where the cstatistic param‑ eter was obtained…”
MethodInfluentialClinical nurses’ work procrastination and smartphone addiction: a potential profile study
Xue, H., Jing, S., Song, X., Zhang, F., Liu, X., & Si, X. (2024) · Frontiers in Psychology · doi:10.3389/fpsyg.2024.1387288 · Cited by 24
“The sample size calculation was based on the 10 events per variable (10 EPV) principle and a general generalized multivariate analysis design, i.e., the sample size was 5–10 times the total number of questionnaire items (Riley et al., 2020).”
MethodChallenges in predictive modelling of chronic kidney disease: A narrative review
Khandpur, S., Mishra, P., Mishra, S., & Tiwari, S. (2024) · World Journal of Nephrology · doi:10.5527/wjn.v13.i3.97214 · Cited by 17
Puntis, S., Whiting, D., Pappa, S., & Lennox, B. (2021) · Translational Psychiatry · doi:10.1038/s41398-020-01172-y · Cited by 17
Hafermann, L., Becher, H., Herrmann, C., Klein, N., Heinze, G., & Rauch, G. (2021) · BMC Medical Research Methodology · doi:10.1186/s12874-021-01373-z · Cited by 20
“Recent development even goes one step further, Riley et al. (2020) state that the calculation of the sample size should also incorporate other factors like the expected predictive performance of the model [22].”
BackgroundHeber, S., Pereyra, D., Schrottmaier, W. C., Kammerer, K., Santol, J., Rumpf, B., Pawelka, E., Hanna, M., Scholz, A., Liu, M., et al. (2022) · Frontiers in Cellular and Infection Microbiology · doi:10.3389/fcimb.2021.795026 · Cited by 17
Lin, H., Pan, X., Feng, Z., Yan, L., Hua, J., Liang, Y., Han, C., Xu, Z., Wang, Y., Wu, L., et al. (2022) · Journal of Translational Medicine · doi:10.1186/s12967-022-03458-9 · Cited by 17
“Hence, the maximum number of candidate risk factors was determined as 7 based on the number of events in the discovery cohort, to ensure that there were at least 10 events per candidate predictor (10 EPP rule [26]).”
BackgroundCollins, E., Galipeau, Y., Arnold, C. R., Bosveld, C. J., Heiskanen, A., Keeshan, A., Nakka, K. K., Shir-Mohammadi, K., Bissonnette, F. S.-D., Tamblyn, L., et al. (2022) · BMJ Open · doi:10.1136/bmjopen-2022-062187 · Cited by 16
COVID-19 prediction models should adhere to methodological and reporting standards
Collins, P. G. S., van Smeden, M., & Riley, R. D. (2020) · European Respiratory Journal · doi:10.1183/13993003.02643-2020 · Cited by 17
Yoon, H., Kim, H. J., Kim, Y., Lee, H., Kim, B. R., Oh, H., Park, H., & Lee, H. (2024) · British Journal of Anaesthesia · doi:10.1016/j.bja.2024.01.030 · Cited by 17
Huang, J., Zhuang, J., Zheng, H., Yao, L., Chen, Q., Wang, J., & Fan, C. (2024) · Nature and Science of Sleep · doi:10.2147/nss.s453794 · Cited by 16
Liang, E. C., Huang, J. J., Portuguese, A. J., Ortiz‐Maldonado, V., Albittar, A. A., Wuliji, N., Basom, R., Jeon, Y., Wu, Q. V., Torkelson, A., et al. (2024) · Blood Advances · doi:10.1182/bloodadvances.2024014455 · Cited by 17
“20 Model speci fi cation and variable selection were based on recommendations by Riley et al. 21 Brie fl y, based on a prevalence of severe eICAHT of 16%, shrinkage factor of 0.9, Cox-Snell R squared statistic of 0.1, and multiplicative margin of error of 1.1, the minimum sample size required for new multivariable devel…”
InfluentialMa, R., Fan, X., Tao, X., Zhang, W., & Li, Z. (2025) · BMC Oral Health · doi:10.1186/s12903-025-05428-1 · Cited by 16
“According to related studies [24], the sample size for a risk prediction model should be at least five to ten times the number of independent variables.”
OnRAMP for Regulating Artificial Intelligence in Medical Products
Higgins, D. C. (2021) · Advanced Intelligent Systems · doi:10.1002/aisy.202100042 · Cited by 19
Decision tree‐based rules outperform risk scores for childhood asthma prognosis
Owora, A. H., Tepper, R. S., Ramsey, C. D., & Becker, A. B. (2021) · Pediatric Allergy and Immunology · doi:10.1111/pai.13530 · Cited by 16
Lohman, E. A. J. D. S., de Bitter, T. J. J., Hannink, G., Wietsma, M. F. T., Vink‐Börger, E. M., Nagtegaal, I. D., Hugh, T. J., Gill, A. J., Bhimani, N., Ahadi, M. S., et al. (2021) · Annals of Surgery · doi:10.1097/sla.0000000000005154 · Cited by 16
Nishioka, N., Kobayashi, D., Kiguchi, T., Irisawa, T., Yamada, T., Yoshiya, K., Park, C., Nishimura, T., Ishibe, T., Yagi, Y., et al. (2021) · Resuscitation · doi:10.1016/j.resuscitation.2021.09.027 · Cited by 16
Cheng, X., Lei, X., Wu, H., Luo, H., Fu, X., Gao, Y., Wang, X., Zhu, Y., & Yan, J. (2022) · Scientific Reports · doi:10.1038/s41598-022-10002-8 · Cited by 16
Emura, T., Michimae, H., & Matsui, S. (2022) · Entropy · doi:10.3390/e24050589 · Cited by 16
“For this reason, the CI is provided only to show the variability of the prediction results, not as a tool to determine the sample size [46].”
MethodWijeysundera, D. N., Alibhai, S. M. H., Ladha, K. S., Puts, M. T. E., Chesney, T. R., Daza, J. F., Ehtesham, S., Hladkowicz, E., Lebovic, G., Mazer, C. D., et al. (2022) · BMJ Open · doi:10.1136/bmjopen-2022-062524 · Cited by 18
“Recent research on sample sizes to develop robust prediction models, 49 which was published after initiation of the FIT After Surgery study, suggests that this sample size estimate is likely conservative.”
Stephens, A., Allardyce, J., Weavers, B., Lennon, J., Jones, R. B., Powell, V. E., Eyre, O., Potter, R., Escott‐Price, V., Osborn, D., et al. (2022) · Journal of Child Psychology and Psychiatry · doi:10.1111/jcpp.13704 · Cited by 16
Ubels, S., Klarenbeek, B. R., Verstegen, M. H. P., Bouwense, S. A. W., Griffiths, E. A., van Workum, F., Rosman, C., Hannink, G., & the TENTACLE—Esophagus Collaborative Group (2022) · Diseases of the Esophagus · doi:10.1093/dote/doac081 · Cited by 15
Du, X., Wen, S., Shi, R., Xia, J., Wang, R., Zhang, Y., Pan, B., Wu, X., Zhu, W., Feng, J., et al. (2023) · BMC Cancer · doi:10.1186/s12885-023-10502-4 · Cited by 17
“We calculated the sample size of the multivariable Cox regression model for patients’ overall survival using the previously reported method [25].”
MethodYu, J., Liu, X., Zhu, Z., Yang, Z., He, J., Zhang, L., & Lu, H. (2023) · Frontiers in Cardiovascular Medicine · doi:10.3389/fcvm.2023.1138234 · Cited by 16
“A small sample size may result in model overfitting and inaccurate predictions (45, 46).”
Backgroundvan Rijn–Dekker, M. I., van Luijk, P., Schuit, E., van der Schaaf, A., Langendijk, J. A., & Steenbakkers, R. J. H. M. (2023) · International Journal of Radiation Oncology*Biology*Physics · doi:10.1016/j.ijrobp.2023.04.034 · Cited by 16
Predicting Outcomes Following Endovascular Abdominal Aortic Aneurysm Repair Using Machine Learning
Li, B., Verma, R., Beaton, D., Tamim, H., Hussain, M. A., Hoballah, J. J., Lee, D. S., Wijeysundera, D. N., de Mestral, C., Mamdani, M., et al. (2023) · Annals of Surgery · doi:10.1097/sla.0000000000005978 · Cited by 16
“25 Our cohort of 16,282 patients with 390 primary events meets this sample size requirement.”
BackgroundLi, B., Verma, R., Beaton, D., Tamim, H., Hussain, M. A., Hoballah, J. J., Lee, D. S., Wijeysundera, D. N., de Mestral, C., Mamdani, M., et al. (2023) · Journal of Vascular Surgery · doi:10.1016/j.jvs.2023.07.006 · Cited by 18
Metadata
- Authors
- Riley, R. D., Ensor, J., Snell, K. I. E., Harrell, F. E., Martin, G. P., Reitsma, J. B., Moons, K. G. M., Collins, G., & van Smeden, M.
- Affiliations
- Keele University (GB)
- Vanderbilt University (US)
- Manchester Academic Health Science Centre (GB)
- University Medical Center Utrecht (NL)
- Corresponding author
- Riley, Richard D
- ORCID
- Venue
- BMJ
- Publisher
- BMJ
- Published
- 2020-03-18
- Volume
- 368
- Pages
- m441
- ISSN
- 1756-1833 (ISSN-L)
- OpenAlex
- W3012413426
- Cited by
- 2,917
- References
- 80
- Citations by year
- 2026: 863 · 2025: 606 · 2024: 531 · 2023: 402 · 2022: 275 · 2021: 174 · 2020: 58
- FWCI
- 160.59
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Licence
- www.bmj.com/company/legal-information/terms-conditions/legal-information/tdm-licencepolicy (tdm)
- Locations
- BMJ (publishedVersion)
- PubMed (publishedVersion)
- Research Explorer (The University of Manchester) (publishedVersion, other-oa)
- Keele Research Repository (Keele University) (submittedVersion, cc-by)
- Utrecht University Repository (Utrecht University) (submittedVersion, other-oa)
- HighWire Press Open Archive (submittedVersion)
- University of Birmingham Research Portal (University of Birmingham) (submittedVersion)
- Funders
- Georgia Clinical and Translational Science Alliance (UL1TR002243)
- Cancer Research UK (27294)
- National Institute for Health and Care Research (SPCR-142)
- Department of Health and Social Care
- Nederlandse Organisatie voor Wetenschappelijk Onderzoek (91208004, 918.10.615, project 9120.8004)
- National Institutes of Health (UL1TR002243)
- NIHR School for Primary Care Research
- National Center for Advancing Translational Sciences (TR002243)
- Topics
- Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Epidemiology
- Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
- Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Clinical Trials
- Keywords
- sample size determination, clinical prediction model, model development, prediction accuracy, prognostic model, diagnostic model, small sample size
- MeSH terms
- Clinical Decision-Making, Forecasting, Humans, Models, Theoretical, Sample Size
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