Estimating pairwise overlap in umbrella reviews: Considerations for using the corrected covered area ( CCA ) index methodology
Open accessAbstract
Umbrella reviews (reviews of systematic reviews) are increasingly used to synthesize findings from systematic reviews. One important challenge when pooling data from several systematic reviews is publication overlap, that is, the same primary publications being included in multiple reviews. Pieper et al. have proposed using the corrected covered area (CCA) index to quantify the degree of overlap between systematic reviews to be pooled in an umbrella review. Recently, this methodology has been integrated in Excel‐ or R‐based tools for easier use. In this short letter, we highlight an important consideration for using the CCA methodology for pairwise overlap assessment, especially when reviews include varying numbers of primary publications, and we urge researchers to fine‐tune this method and exercise caution when review exclusion decisions are based on its output.
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CCA analysis of strength across all included reviews showed only moderate overlap, defined as between 6% and 10% of primary papers appearing in two or more reviews.
“CCA analysis of strength across all included reviews showed only “moderate” overlap, defined as between 6% and 10% of primary papers appearing in two or more reviews (27).”
From American College of Sports Medicine Position Stand. Resistance Training Prescription for Muscle Function, Hypertrophy, and Physical Performance in Healthy Adults: An Overview of Reviews (2026) · cites this paper as [27]
The Introduction defines a CCA of 6%–10% as moderate overlap. It does not report an analysis of strength across the citing paper’s included reviews, and its formula does not define CCA as the percentage of primary papers appearing in two or more reviews. Section 2 uses hypothetical examples rather than reporting that result. (LLM, conf=0.86)
Experimental — accuracy not yet measuredThe corrected covered area (CCA) index was used to quantify the degree of overlap between systematic reviews.
“We employed the corrected covered area (CCA) index to quantify the degree of overlap between systematic reviews to be pooled in an overview of reviews (27).”
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Systematic review finds overlapping reviews were not mentioned in every other overview
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“Therefore, to quantify the degree of publication overlap in umbrella reviews, Pieper et al.(4) have proposed using the corrected covered area (CCA) index.”
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Graphical Representation of Overlap for OVErviews: GROOVE tool
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“(18).”
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Plascak, J. J., Ard, K., Paskett, E., & Tarver, W. L. (2026) · Preventive Oncology & Epidemiology · doi:10.1080/28322134.2026.2715789
Triggers and Modifiers of Acute Coronary Events and Implications for Practice: An Umbrella Review.
Hunt, L., Riegel, M., Tofler, G., Heighes, P., Shi, W.-D., & Buckley, T. (2026) · Journal of Advanced Nursing · doi:10.1111/jan.70777
Bruno, J., Montoro-Bombú, R., Thapa, R. K., & Sarmento, H. (2026) · Sports Medicine · doi:10.1007/s40279-026-02538-w
Bano, B., Cristofalo, D., Prina, E., Patania, F., Mazzé, F., Ostuzzi, G., Barbui, C., Albanese, E., & Purgato, M. (2026) · Clinical Psychology Review · doi:10.1016/j.cpr.2026.102804
Castillo, F., Morel-Marambio, M., Mora, F. P., Ortiz-Muñoz, L., Bustamante, G., Fajre, F., & Cea, G. (2026) · The Neuroscientist · doi:10.3390/neurosci7050107
“CCA was used solely to characterize overlap and inform interpretation, rather than as an eligibility criterion, because its magnitude may also be influenced by differences in the number of primary studies included across reviews [47].”
Wang, W.-L., Li, Y.-Z., Liu, C.-R., Chen, C., Chen, M., Thabane, L., Sun, X., & Tan, J. (2026) · iMetaMed · doi:10.1002/imm3.70060
Shao, Y.-Q., Yin, S.-Y., Wu, T.-Y., Zou, C., Yang, J.-Y., Feng, P., Zhou, Y.-J., & Sun, G.-J. (2026) · International Journal for Vitamin and Nutrition Research · doi:10.31083/ijvnr49111
Kim, R., Lee, H.-J., & Kang, N. (2026) · Symmetry · doi:10.3390/sym18091484
Sha, T.-N., Liao, Z.-H., Yuan, T.-W., Wang, Y., Liang, W., Xu, E.-Y., Zhang, X.-L., Li, Z.-W., Zhao, J.-K., Müller, O., et al. (2026) · International Journal of Infectious Diseases · doi:10.1016/j.ijid.2026.109160
Zhang, X.-Y., Wang, Y., Guan, Y., & Qu, R. (2026) · Clinical and Translational Oncology · doi:10.1007/s12094-026-04535-x
Tiga-Loza, D. C., Urrea-Vega, E. A., Rivera-Carvajal, R., Álvarez-Anaya, W. A., Buitrago-Buitrago, J. A., Hernández-Martínez, A. M., & Camacho-López, P. (2026) · BMC Geriatrics · doi:10.1186/s12877-026-07933-6
“The level of overlap was interpreted according to the criteria proposed by Pieper and Kirvalidze [35, 36], where CCA values of 0–5 indicate slight overlap, 6–10 moderate overlap, 11–15 high overlap, and > 15 very high overlap.”
Gutteridge, D. S., Babu, D., Stasinopoulos, J., Calder, A., Bakker, M., Marotti, S., Patrickson, B., Macolino, K., Martín, C., Zhao, L.-J., et al. (2026) · PLOS Digital Health · doi:10.1371/journal.pdig.0001583
“Overlaps in primary studies between systematic reviews were summarised using the corrected covered area (CCA) index (CCA = (N-r)/(r x c)-r; where N is the total number of primary studies (including duplicates); r is the number of unique primary studies; and c is the number of reviews) [40].”
Yan, L.-T., Ahmad, M. A., Peng, Y., Lee, C.-L., & Singh, D. K. A. (2026) · IIUM Medical Journal Malaysia · doi:10.31436/imjm.v25i03.2978
Nair, A., Mistry, T., & Borkar, N. B. (2026) · Saudi Journal of Anaesthesia · doi:10.4103/sja.sja_998_25
“The corrected covered area (CCA) was calculated to quantify overlap [28] : CCA = (Nr – Ns)/{(Np x Ns) – Ns} where Nr = total number of RCTs included, Ns = total number of unique studies, and Np = number of systematic reviews and meta‑analyses included.”
Ali, A. R., Kumar, P., Patnana, A., Shanmugam, S., Chugh, A., & Chaudhry, K. (2026) · Special Care in Dentistry: managing special patients, settings, and situations · doi:10.1111/scd.70235
Hsu, C.-Y., Hussein, H. Y., Al‐Akkam, K. A., Gajjar, T. B., Almohamadi, H., Нодир, Х., Shukla, S. K., Radhi, S. H., Smerat, A., & Iqbal, M. S. (2026) · Inflammopharmacology · doi:10.1007/s10787-026-02266-7
“When over - lap was substantial (CCA > 15%), the most comprehensive and highest-quality meta-analysis was prioritized in report - ing (Kirvalidze et al. 2023 ).”
Wynne, R., Dharmalingam, R., Omarit, R., Eastwood, G., & Matthews, S. (2026) · Australian Critical Care · doi:10.1016/j.aucc.2026.101631
Bernardo, L. C., Velozo, B. C., Castro, M. C. N. E., Gaspar, S. M. D. S., & Abbade, L. P. F. (2026) · Revista de Enfermagem UFPE On Line · doi:10.5205/1981-8963.2026.268441
Prehabilitation and postoperative outcomes in colorectal surgery: an umbrella review
Tadesse, M. A., Alimawu, A. A., Matrisch, L., Abebe, M. M., Techale, K., Bekele, Z., & Alemu, E. A. (2026) · Journal of Anesthesia Analgesia and Critical Care · doi:10.1186/s44158-026-00418-3
“The degree of overlap is classified as 0%–5% ‘slight overlap’, 6%–10% ‘moderate overlap’, 11%–15% ‘high overlap’, and > 15% is considered as ‘very high overlap’[47].”
Interventions Applied at Slaughterhouse to Reduce Campylobacter spp. Load
Adams, L., Hale, A., Wheeler, L., Gadaria, A., Jackson, J., Atoyebi, O., Kintz, E., Ford, I., Wilson, A. J., & Amanatidou, E. (2026) · FSA Research and Evidence · doi:10.46756/001c.161470
Luijk, A., Bricca, A., Mortensen, S. R., Holm, P., Zanger, G., Simonÿ, C., Skou, S., Lund, T., & Tang, L. (2026) · British Journal of Sports Medicine · doi:10.1136/bjsports-2025-110444
“66 100 However, using a lower or higher cut-point could potentially affect our findings.”
Li, F.-B., Li, Q.-F., Huang, J.-F., Li, X.-C., & Lu, Z.-S. (2026) · Frontiers in Psychology · doi:10.3389/fpsyg.2026.1806563
“The Corrected covered area (CCA) method was used to assess the degree of overlap among the trials included in each systematic review and meta-analysis (Kirvalidze et al., 2023).”
COVID-19, climate change, and air pollution: a syndemic umbrella review
Jung, E., Lee, E.-Y., & Shin, H. (2026) · City and Environment Interactions · doi:10.1016/j.cacint.2026.100381
Denusik, L., Choi, L., Binns, A. V., Rushton, A., & Oram, J. (2026) · Autism & Developmental Language Impairments · doi:10.1177/23969415261483566
An overview of reviews of Angiotensin II in distributive shock
Desfosses, M., & Røislien, J. (2026) · BMC Anesthesiology · doi:10.1186/s12871-026-03797-w
“Primary study overlap among the included reviews was quantified by the primary reviewer (MD) and verified by a second reviewer (HA) using the corrected covered area (CCA) index [9, 13].”
Reflexology for blood pressure control: A comprehensive evidence-based umbrella review
Shamsikhani, S., & Hosseini, M. (2026) · Journal of Integrative Nursing · doi:10.4103/jin.jin_17_26
Jiang, B., Li, Y., Zhong, W.-L., Zou, Y.-N., Chen, B.-C., & Yu, B. (2026) · Journal of Translational Medicine · doi:10.1186/s12967-026-07789-9
“To assess redundancy across the included meta-analyses, we quantified the overlap of primary studies using the CCA index, as described by Pieper et al. and implemented in the GROOVE (Graphical Representation of Overlap for OVErviews) tool [26, 27].”
Mohale, T. K., ten Ham-Baloyi, W., Baloyi, O., & Gumede, E. Z. (2026) · JMIR Research Protocols · doi:10.2196/94779
“Overlap will be evaluated using citation matrices and CCA calculations, with guidance from recent methodological recommendations for pairwise overlap assessment in umbrella reviews [28,29].”
Effectiveness of Telerehabilitation After Total Knee Arthroplasty: An Umbrella Review.
Xu, H., Lou, V. W. Q., Guo, Z., Di, R., Zhang, X., & Liu, Y.-J. (2026) · Journal of Arthroplasty · doi:10.1016/j.arth.2026.02.041
Zhao, X., Zou, R.-J., Miao, H.-R., Chang, X., Chinda, K., Chen, F., Zhang, M., Zhuo, J., Sun, X., Chen, Y., et al. (2026) · Reviews in cardiovascular medicine · doi:10.31083/rcm46055
“The corrected covered area (CCA) quantifies the degree of overlap in the included literature [24].”
Meijer, T. L., van Opdorp, A., & Markus, W. (2026) · Psychedelics · doi:10.1016/j.psyche.2026.100014
Childhood Anemia and Its Associated Factors in Africa: Umbrella Review
Wondifraw, E. B., Wudu, M. A., Getaneh, F. B., Gezie, H., & Wondie, K. Y. (2026) · Sage Open Pediatrics · doi:10.1177/30502225261502360
Żywiec, W., Dorota, A., Dorota, M., Karaban, K., Maryniak, N., & Rzeszutek, J. (2026) · International Journal of Innovative Technologies in Social Science · doi:10.31435/ijitss.1(49).2026.4981
Virtual Reality in Chronic Conditions: An Umbrella Review
Marcomini, I., Villa, G., Ingrande, L., Latini, G., Poliani, A., Manara, D., & Rosa, D. (2026) · Nursing Reports · doi:10.3390/nursrep16020057
“The degree of overlap was quantified using the Corrected Covered Area (CCA), calculated according to the method proposed by Kirvalidze et al. [18].”
Torabiardakani, K., Sawant, S. B., Bravo-Soto, G., Montalva-Romero, D., Couban, R., Chu, A. E., Buckley, N., Guyatt, G., Juurlink, D., Busse, J., et al. (2026) · Clinical and public health guidelines · doi:10.1002/gin2.70058
Relationship Between Floppy Eyelid Syndrome and Obstructive Sleep Apnea Syndrome: An Umbrella Review
Napoli, G. T. O., Lobato, D. M., Albertini, F., & Machado, A. (2026) · Journal of Ophthalmology · doi:10.1155/joph/6084912
“Equation (1) shows CCA calculation [25].”
InfluentialAcupuncture for fibromyalgia syndrome: an overview of systematic reviews and meta-analyses
Choi, T., Jun, J. H., Lee, H. R., & Lee, M. S. (2025) · Frontiers in Medicine · doi:10.3389/fmed.2025.1712065
The Role of Minerals in COVID-19: An Umbrella Review
van Deventer, C., Konn, C., Doherty, M., & Purdy, R. (2023) · CAND Journal · doi:10.54434/candj.164
“64 Almost all of the studies included in our review had a low risk of bias based on quality assessment.”
Background
- Authors
- Kirvalidze, M., Abbadi, A., Dahlberg, L., Sacco, L. B., Calderón‐Larrañaga, A., & Morin, L.
- Affiliations
- Stockholm University (SE)
- Dalarna University (SE)
- Inserm (FR)
- Corresponding author
- Kirvalidze, Mariam
- ORCID
- Venue
- Research Synthesis Methods
- Publisher
- Wiley
- Published
- 2023-07-27
- Volume
- 14
- Issue
- 5
- Pages
- 764-767
- ISSN
- 1759-2879 (ISSN-L)
- 1759-2887
- OpenAlex
- W4385330471
- Cited by
- 102
- References
- 11
- Citations by year
- 2026: 61 · 2025: 34 · 2024: 5 · 2023: 2
- FWCI
- 18.98
- Type
- journal article
- Language
- en
- Open access
- hybrid
- doi.org
- Licence
- Locations
- Research Synthesis Methods (publishedVersion, cc-by)
- PubMed (publishedVersion)
- Dalarna University College Electronic Archive (submittedVersion, other-oa)
- Funders
- Forskningsrådet om Hälsa, Arbetsliv och Välfärd (2020‐01544)
- Topics
- Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
- Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › scientometrics and bibliometrics research
- Social Sciences › Psychology › Experimental and Cognitive Psychology › Psychology Research and Bibliometrics
- Keywords
- umbrella review, systematic reviews, data pooling
- MeSH terms
- Systematic Reviews as Topic, Humans, Research Design, Research Personnel
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