Mattei 2014 — PASI ↔ DLQI correlation in biologic RCTs (r² = 0.80)
Citation
Mattei PL, Corey KC, Kimball AB. Psoriasis Area Severity and Index (PASI) and the Dermatology Life Quality Index (DLQI): the correlation between disease severity and psychological burden in patients treated with biological therapies. J Eur Acad Dermatol Venereol. 2014 Mar;28(3):333–337. DOI: 10.1111/jdv.12106.
Study design and population
PRISMA systematic review of 13 biologic RCTs in moderate-to-severe psoriasis that reported both PASI and DLQI; thousands of patients pooled at trial-arm level.
Reported metrics
- r² = 0.80 between PASI % improvement and DLQI change from baseline through weeks 10–16 (95 % CI not reported — flag)
- Arms achieving ≥ 75 % mean PASI reduction produced a DLQI band 3 → band 1 shift across nine treatment arms
- DLQI MCID = 3.2
Surrogate-to-outcome linkage
Highest-level aggregate evidence that PASI improvement explains ~80 % of the variance in DLQI improvement at trial-arm level. This is the quantitative anchor for the severity-score → HRQoL surrogate-to-outcome claim in psoriasis. Converts the regulatory-acceptance evidence (EMA 2004) into a measurable effect size.
CRIT1–7 appraisal
| Criterion | Score | Justification |
|---|---|---|
| CRIT1 Relevance | 3 | Direct — PASI ↔ DLQI linkage, the core psoriasis surrogate-to-outcome claim. |
| CRIT2 Methodology | 3 | PRISMA-aligned systematic review of 13 RCTs. |
| CRIT3 Reporting | 2 | r² and band-shift reported; 95 % CI for r² not in source (flag). |
| CRIT4 Applicability | 3 | Biologic-treated moderate-to-severe psoriasis — exact intended-use population. |
| CRIT5 Evidence weight | 3 | Systematic review of RCTs. |
| CRIT6 Risk of bias | 2 | Trial-arm-level (not individual-patient-level) correlation; potential selective reporting in constituent trials. |
| CRIT7 Contribution | 3 | Core aggregate anchor for the psoriasis surrogate-to-outcome linkage. |
Aggregate: very strong.
Limitations and notes
Trial-arm-level pooling inflates r² relative to individual-patient Spearman ρ (typically 0.40–0.57 at patient level). The CER should state this limitation explicitly.
Strength as anchor
Very strong for the quantitative linkage claim in psoriasis. Pairs with Revicki 2008 (patient-level PASI → DLQI monotonic gradient in adalimumab RCTs) to span trial-arm and individual-patient levels.