I read Liu et al’s [1] abbreviation of the Quality of Life Instrument for Chronic Diseases–Benign Prostatic Hyperplasia (BPH)–specific module with interest. Deciding a short form’s length from generalizability theory rather than by consensus is a welcome discipline, and a seven-item instrument is attractive for a 10-min consultation. My points concern what the Specific Domain-7 (SPD-7) measures and what it can be used for.
The authors validate the SPD-7 through several complementary analyses (classical test theory, item response theory, and generalizability theory), and I do not question that internal evaluation. My concern is narrower: the only criterion-related evidence offered is the correlation with the parent Specific Domain-16 (SPD-16) (0.910 for the total; 0.98 and 0.78 for the facets), yet those seven items are part of that 16-item total. The parent α of 0.881 implies a mean interitem correlation near 0.32; under the simplifying assumption of approximately equal interitem correlations, any seven of the 16 items would be expected to correlate with the total at roughly 0.93, and the same calculation, applied to the SPD-7 α of 0.850, is consistent with its reported mean interitem correlation of 0.445.
Therefore, this correlation is largely a function of nesting and provides limited information about whether these seven items were well chosen [2]. No comparison with the International Prostate Symptom Score (IPSS), its quality-of-life item, or the BPH Impact Index is reported [3], so an SPD-7 score cannot yet be placed against anything already in use.
Second, the reduction removed some of the most clinically informative items. BPH15 asks whether the patient has given up recreational activities because of frequent urination, and BPH16 asks whether he avoids going out for fear of finding a toilet; both describe a man who reorganizes his life around his bladder-related symptoms, yet they were deleted because they overlapped with the general module. BPH6, “Are you afraid of hematuria?”, was removed because responses were sparse and hematuria was judged uncommon, although the fear it measures need not track how often bleeding occurs.
Item reduction of this kind is expected to incorporate patient input rather than expert judgment alone [2]. A further asymmetry is internal to the paper’s own data: daytime frequency (BPH2) was deleted, whereas nocturia (BPH4) was retained, although Table 4 records BPH2 as satisfying six of the seven screening criteria against five for BPH4. I recognize that the core panel removed BPH2 on semantic and clinical grounds, and I would welcome the authors’ clarification of how that judgment was weighed against the item’s stronger quantitative profile.
Third, the SPD-7 is recommended for dynamic monitoring and treatment evaluation, yet the study is cross-sectional: no test-retest reliability, responsiveness, or minimal important difference is reported, so a clinician cannot say what change at follow-up matters [4]. Although the authors rightly acknowledge in their limitations the need for external validation in independent samples, the concurrent recommendation of the SPD-7 for routine use and dynamic monitoring appears premature, given a purely cross-sectional design.
These concerns could be addressed by an outpatient cohort administering the SPD-7 alongside the IPSS and its bother item, together with a repeat administration to establish test-retest reliability and a minimal important difference. More generally, where a short form is nested inside its parent, that correlation is better reported as an arithmetic property of the instrument than as concurrent validity, and validation in an independent sample should precede a recommendation for routine practice. I would welcome the authors’ view.
Conflicts of interest: The authors have nothing to disclose.
Declaration of generative AI and AI-assisted technologies in the writing process: During the preparation of this work, the author used a large language model (Gemini, Google) to assist with language editing of the text. After using this tool, the author reviewed and edited the content as needed and takes full responsibility for the content of the publication. No analysis, data, or interpretation was generated by the tool.