31 March 2025
To the Editors of the Journal of Alzheimer's Disease,
Dr. Yang and colleagues published a manuscript titled "Rapid Cognitive Assessment: Accuracy and Discriminant Validity of Mini-Cog and Process-Based Clock Drawing" in the January issue of the Journal of Alzheimer's Disease [1]. The authors concluded that the Mini-Cog3 was an effective screening method for the rapid and accurate detection of cognitive dysfunction in patients with mild cognitive impairment and Alzheimer's disease.
In Table 3, the authors list the AUC, specificity, sensitivity, positive predictive value, negative predictive value, positive likelihood ratio (PLR), and negative likelihood ratio (NLR) for the various Mini-Cog tests and the Clock Drawing Test (CDT). Unfortunately, the NLR is miscalculated, which misleads readers and alters the study's findings. The correct formula for the negative likelihood ratio is:
NLR=1−SensitivitySpecificity
[2,3]. Based on this, the NLR for the minimally cognitively impaired group should be as follows:
- Mini-Cog1: 0.518
- Mini-Cog2: 0.457
- CDT: 0.2
- Mini-Cog3: 0.23
These calculations indicate that the CDT has the highest value in screening out mild cognitive impairment, and the Mini-Cog evaluation does not add significant value to the CDT.
For the Alzheimer's group, the correct NLR values are:
- Mini-Cog1: 0.134
- Mini-Cog2: 0.135
- CDT: 0.24
- Mini-Cog3: 0.164
Clinically, this means that a normal CDT reduces the probability of mild cognitive impairment by 30% (2). If the CDT is normal, additional screening with the Mini-Cog does not provide additional diagnostic value. However, if the CDT is abnormal, the Mini-Cog increases the probability of mild cognitive impairment to 35-40%.
When screening for Alzheimer's disease, a normal CDT, additional testing using the Mini-Cog3 increases the probability that the patient does not have Alzheimer's dementia by 10% compared to the CDT alone. Conversely, an abnormal Mini-Cog3 increases the probability of Alzheimer's disease by 40% (2). These findings suggest that, in the sequence of testing, the CDT should be administered first. If the CDT is normal, further testing with the Mini-Cog for mild cognitive impairment may not be necessary. An initially normal CDT significantly reduces the likelihood of Alzheimer's disease.
Mellar P Davis MD FCCP FAAHPM
Director of Palliative Medicine, Department of Supportive Oncology
Levine Cancer Institute
1021 Morehead Medical Drive #5300
Charlotte, NC 28204-2990
Email: Mellar.Davis@atriumhealth.org
References
[1] Yang Q, Yang H, Long W, et al. Rapid cognitive assessment: Accuracy and discriminant validity of Mini-Cog and process-based Clock Drawing Test. J Alzheimers Dis 2025; 104: 200-208.
[2] McGee S. Simplifying likelihood ratios. J Gen Intern Med 2002; 17: 646-649.
[3] Davis MP, Soni K and Strobel S. Likelihood ratios: An important concept for palliative physicians to understand. Am J Hosp Palliat Care 2023; 40: 894-899.
Comments
Response to Letter to the Editor from Dr. Davis
Dear Dr. Mellar P. Davis,
Thank you for carefully reviewing our manuscript titled "Rapid Cognitive Assessment: Accuracy and Discriminant Validity of Mini-Cog and Process-Based Clock Drawing Test" published in JAD and for pointing out the miscalculations in the negative likelihood ratio (NLR) values. We are grateful for your expertise and the time you spent examining our work.
Upon reanalysis of our original data, we confirmed that the NLR values in Table 3 were indeed calculated incorrectly, with the numerator and denominator reversed. We deeply regret this oversight, which may have mislead readers. Enclosed, please find the corrected Table 3, with the revised NLR values highlighted in red. The corrected NLR for the Clock Drawing Test (CDT) in diagnosing MCI is 0.21, and for the Mini-Cog3, it is 0.24. The small difference of 0.03 indicates that both tests have similar performance in ruling out MCI. However, the Mini-Cog3 shows a significantly higher area under the curve (AUC) of 0.82 compared to the CDT's AUC of 0.77, demonstrating its superior diagnostic accuracy.
Regarding your suggestion that “in the sequence of testing, the CDT should be administered first, and if the CDT is normal, further testing with the Mini-Cog for mild cognitive impairment may not be necessary,” we would like to clarify. While the CDT can indeed rule out MCI, if the CDT is abnormal, the Mini-Cog3 should not be administered subsequently, as it already includes the CDT. The Mini-Cog3 assessment begins with immediate recall of three words, followed by the CDT, and concludes with delayed recall of the same words. This comprehensive approach, which evaluates both memory recall and executive functions, is completed within a brief 2-3 minutes, making it an efficient tool for clinical settings. Consequently, we advocate for the direct use of the Mini-Cog3 in community screenings for MCI and early-stage Alzheimer’s disease to enhance detection rates without incurring significant time costs.
Given the minimal difference in NLR values and the superior diagnostic accuracy and comprehensive assessment provided by the Mini-Cog3, we maintain our recommendation that the Mini-Cog3 is the preferred tool for the rapid and accurate detection of cognitive dysfunction in patients with MCI and Alzheimer's disease.
Once again, we thank you for your insightful feedback.
Sincerely,
Qian Yang
Corresponding author: Defa Zhu, Department of Geriatric Endocrinology, The First Affiliated Hospital of Anhui Medical University, Hefei, Anhui, China. Email: zdfa0168@sina.com
Qihao Guo, Department of Gerontology, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, China. Email:
The corrected Table 3 is as follows:
- Comment
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