title: Measuring Physical Activity in Juvenile Idiopathic Arthritis: Activity Diary Versus Accelerometer.
abstract: (1) To determine convergent validity of an activity diary (AD) and accelerometer (Actical brand/Phillips-Respironics) in measuring physical activity (PA) in children with juvenile idiopathic arthritis (JIA). (2) To determine how many days give reliable results. (3) To analyze effects of correcting accelerometer data for non-wear.
  
  
  
  Patients with JIA (8-13 yrs) were recruited from 3 Dutch pediatric rheumatology centers. PA was assessed for 7 days with an AD and accelerometer, and was expressed as mean min/day of rest, light PA (LPA), moderate to vigorous PA (MVPA), and PA level (PAL). To analyze convergent validity, intraclass correlation coefficients (ICC) were calculated and paired sample Student t tests were performed. The required number of days to achieve reliable results was calculated using the Spearman-Brown prophecy formula.
  
  
  
  Convergent validity between AD and accelerometer was moderate for rest and PAL (ICC 0.41). ICC for LPA and MVPA were < 0.24. AD overestimated PAL and MVPA compared with the accelerometer. Wearing the accelerometer 7-19 days gave reliable PA estimates on group and individual levels. For the AD, 13-36 days were needed. Adjusting accelerometer data for non-wear resulted in a clinically relevant higher mean number of min/day spent in LPA (effect size 1.12), but not in MVPA (effect size 0.44).
  
  
  
  Convergent validity between AD and accelerometer is moderate to poor. In children with JIA, 1-week assessment with an accelerometer is sufficient to measure PA (all levels) reliably. On an individual level and for clinical use, 3 weeks are required. Additional use of AD enables correction for non-wear of accelerometer data.
authors.affiliation: From the University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Department of Pediatric Rheumatology, and Department for Rehabilitation Medicine, and Department of Oral and Maxillofacial Surgery, Groningen, the Netherlands. w.armbrust@umcg.nl.|W. Armbrust, PhD, University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Department of Pediatric Rheumatology; G.J. Bos, MSc, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine; J.H. Geertzen, PhD, Professor, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine; P.J. Sauer, PhD, Professor, University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital; P.U. Dijkstra, Professor, PhD, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine, and Department of Oral and Maxillofacial Surgery; O.T. Lelieveld, PhD, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine. W. Armbrust and G.J. Bos are co-authors. w.armbrust@umcg.nl.
authors.forename: Wineke
authors.initials: W
authors.lastname: Armbrust
authors.affiliation: From the University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Department of Pediatric Rheumatology, and Department for Rehabilitation Medicine, and Department of Oral and Maxillofacial Surgery, Groningen, the Netherlands.|W. Armbrust, PhD, University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Department of Pediatric Rheumatology; G.J. Bos, MSc, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine; J.H. Geertzen, PhD, Professor, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine; P.J. Sauer, PhD, Professor, University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital; P.U. Dijkstra, Professor, PhD, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine, and Department of Oral and Maxillofacial Surgery; O.T. Lelieveld, PhD, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine. W. Armbrust and G.J. Bos are co-authors.
authors.forename: G J F Joyce
authors.initials: GJFJ
authors.lastname: Bos
authors.affiliation: From the University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Department of Pediatric Rheumatology, and Department for Rehabilitation Medicine, and Department of Oral and Maxillofacial Surgery, Groningen, the Netherlands.|W. Armbrust, PhD, University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Department of Pediatric Rheumatology; G.J. Bos, MSc, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine; J.H. Geertzen, PhD, Professor, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine; P.J. Sauer, PhD, Professor, University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital; P.U. Dijkstra, Professor, PhD, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine, and Department of Oral and Maxillofacial Surgery; O.T. Lelieveld, PhD, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine. W. Armbrust and G.J. Bos are co-authors.
authors.forename: Jan H B
authors.initials: JHB
authors.lastname: Geertzen
authors.affiliation: From the University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Department of Pediatric Rheumatology, and Department for Rehabilitation Medicine, and Department of Oral and Maxillofacial Surgery, Groningen, the Netherlands.|W. Armbrust, PhD, University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Department of Pediatric Rheumatology; G.J. Bos, MSc, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine; J.H. Geertzen, PhD, Professor, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine; P.J. Sauer, PhD, Professor, University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital; P.U. Dijkstra, Professor, PhD, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine, and Department of Oral and Maxillofacial Surgery; O.T. Lelieveld, PhD, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine. W. Armbrust and G.J. Bos are co-authors.
authors.forename: Pieter J J
authors.initials: PJJ
authors.lastname: Sauer
authors.affiliation: From the University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Department of Pediatric Rheumatology, and Department for Rehabilitation Medicine, and Department of Oral and Maxillofacial Surgery, Groningen, the Netherlands.|W. Armbrust, PhD, University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Department of Pediatric Rheumatology; G.J. Bos, MSc, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine; J.H. Geertzen, PhD, Professor, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine; P.J. Sauer, PhD, Professor, University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital; P.U. Dijkstra, Professor, PhD, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine, and Department of Oral and Maxillofacial Surgery; O.T. Lelieveld, PhD, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine. W. Armbrust and G.J. Bos are co-authors.
authors.forename: Pieter U
authors.initials: PU
authors.lastname: Dijkstra
authors.affiliation: From the University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Department of Pediatric Rheumatology, and Department for Rehabilitation Medicine, and Department of Oral and Maxillofacial Surgery, Groningen, the Netherlands.|W. Armbrust, PhD, University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Department of Pediatric Rheumatology; G.J. Bos, MSc, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine; J.H. Geertzen, PhD, Professor, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine; P.J. Sauer, PhD, Professor, University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital; P.U. Dijkstra, Professor, PhD, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine, and Department of Oral and Maxillofacial Surgery; O.T. Lelieveld, PhD, University of Groningen, University Medical Center Groningen, Department for Rehabilitation Medicine. W. Armbrust and G.J. Bos are co-authors.
authors.forename: Otto T H M
authors.initials: OTHM
authors.lastname: Lelieveld
mesh_terms: D061725:Accelerometry; D000293:Adolescent; D001171:Arthritis, Juvenile / Q000503:physiopathology*; D002648:Child; D003430:Cross-Sectional Studies; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D057185:Sedentary Behavior; D057566:Self Report
keywords: JUVENILE IDIOPATHIC ARTHRITIS; PATIENT-REPORTED OUTCOME; PHYSICAL ACTIVITY