OBJECTIVES: To evaluate the psychometric properties of scores on a twice-daily electronic diary (eDiary) developed to measure bowel movement (BM) characteristics (frequency, consistency, completeness, straining) associated with functional constipation (FC) in a pediatric population.

METHODS: Data from a phase 3, multicenter, randomized, double-blind, placebo-controlled study (LIN-MD-64) of linaclotide 72 μg in 6-to-17-year-olds (n=328) meeting Rome III criteria for child/adolescent FC were used. Patient global impression of severity (PGIS) items assessed “pooping” problems every 7 days. Participants who met entry criteria entered the 12-week study period utilizing the eDiary. The study primary endpoint was 12-week change from baseline (CFB) in weekly spontaneous BM (SBM) frequency; the secondary endpoint was CFB in stool consistency (pediatric Bristol Stool Form Scale [p-BSFS]). Test-retest reliability was assessed through intraclass correlation coefficients (ICC), construct validity using convergent and discriminant validity correlations and known-groups methods, and responsiveness through Guyatt’s responsiveness statistic (GRS). PGIS items were anchors used for estimating within-patient meaningful change thresholds (MCTs).

RESULTS: ICC for SBMs showed good test-retest reliability (ICC=0.91); ICC for stool consistency showed moderate test-retest reliability (ICC=0.56) at weeks 11 to 12. SBMs were strongly correlated with complete SBMs (CSBMs) (r=0.82) and moderately correlated with straining (r=‑0.32), Stool consistency was moderately correlated with straining (r=-0.49), but less correlated with SBMs (r=0.22) and CSBMs (r=0.21). Construct validity using known-groups found significant differences for SBM frequency rate and stool consistency by participant PGIS scores at week 12 (P<0.001). For PGIS items, GRS was small for SBMs and large for stool consistency. MCTs were estimated to be a CFB of ≥2 SBMs and 0.8-1.7 for p-BSFS.

CONCLUSIONS: This evaluation provides sufficient evidence for reliability, validity, and responsiveness of the eDiary to measure SBMs and stool consistency and provides guidance for interpreting meaningful within-patient change on these scores.