title: Longitudinal accuracy of web-based self-reported weights: results from the Hopkins POWER Trial.
abstract: BACKGROUND
  Websites and phone apps are increasingly used to track weights during weight loss interventions, yet the longitudinal accuracy of these self-reported weights is uncertain.
  
  
  OBJECTIVE
  Our goal was to compare the longitudinal accuracy of self-reported weights entered online during the course of a randomized weight loss trial to measurements taken in the clinic. We aimed to determine if accuracy of self-reported weight is associated with weight loss and to determine the extent of misclassification in achieving 5% weight loss when using self-reported compared to clinic weights.
  
  
  METHODS
  This study examined the accuracy of self-reported weights recorded online among intervention participants in the Hopkins Practice-Based Opportunities for Weight Reduction (POWER) trial, a randomized trial examining the effectiveness of two lifestyle-based weight loss interventions compared to a control group among obese adult patients with at least one cardiovascular risk factor. One treatment group was offered telephonic coaching and the other group was offered in-person individual coaching and group sessions. All intervention participants (n=277) received a digital scale and were asked to track their weight weekly on a study website. Research staff used a standard protocol to measure weight in the clinic. Differences (self-reported weight - clinic weight) indicate if self-report under (-) or over (+) estimated clinic weight using the self-reported weight that was closest in time to the clinic weight and was within a window ranging from the day of the clinic visit to 7 days before the 6-month (n=225) and 24-month (n=191) clinic visits. The absolute value of the differences (absolute difference) describes the overall accuracy.
  
  
  RESULTS
  Underestimation of self-reported weights increased significantly from 6 months (mean -0.5 kg, SD 1.0 kg) to 24 months (mean -1.1 kg, SD 2.0 kg; P=.002). The average absolute difference also increased from 6 months (mean 0.7 kg, SD 0.8 kg) to 24 months (mean 1.3, SD 1.8 kg; P<.001). Participants who achieved the study weight loss goal at 24 months (based on clinic weights) had lower absolute differences (P=.01) compared to those who did not meet this goal. At 24 months, there was 9% misclassification of weight loss goal success when using self-reported weight compared to clinic weight as an outcome. At 24 months, those with self-reported weights (n=191) had three times the weight loss compared to those (n=73) without self-reported weights (P<.001).
  
  
  CONCLUSIONS
  Underestimation of weight increased over time and was associated with less weight loss. In addition to intervention adherence, weight loss programs should emphasize accuracy in self-reporting.
  
  
  BACKGROUND
  ClinicalTrials.gov: NCT00783315; http://clinicaltrials.gov/show/NCT00783315 (Archived by WebCite at http://www.webcitation.org/6R4gDAK5K).
authors.affiliation: Department of Kinesiology, Towson University, Towson, MD, United States. gjerome@towson.edu.
authors.forename: Gerald J
authors.identifier: http://orcid.org/0000-0003-0612-2626
authors.initials: GJ
authors.lastname: Jerome
authors.forename: Arlene
authors.identifier: http://orcid.org/0000-0001-9784-7854
authors.initials: A
authors.lastname: Dalcin
authors.forename: Janelle W
authors.identifier: http://orcid.org/0000-0001-7924-5892
authors.initials: JW
authors.lastname: Coughlin
authors.forename: Stephanie
authors.identifier: http://orcid.org/0000-0002-6960-6073
authors.initials: S
authors.lastname: Fitzpatrick
authors.forename: Nae-Yuh
authors.identifier: http://orcid.org/0000-0001-6513-9730
authors.initials: NY
authors.lastname: Wang
authors.forename: Nowella
authors.identifier: http://orcid.org/0000-0002-1165-0565
authors.initials: N
authors.lastname: Durkin
authors.forename: Hsin-Chieh
authors.identifier: http://orcid.org/0000-0002-5738-0652
authors.initials: HC
authors.lastname: Yeh
authors.forename: Jeanne
authors.identifier: http://orcid.org/0000-0002-1825-0097
authors.initials: J
authors.lastname: Charleston
authors.forename: Thomas
authors.identifier: http://orcid.org/0000-0002-4846-052X
authors.initials: T
authors.lastname: Pozefsky
authors.forename: Gail L
authors.identifier: http://orcid.org/0000-0003-0717-0216
authors.initials: GL
authors.lastname: Daumit
authors.forename: Jeanne M
authors.identifier: http://orcid.org/0000-0003-1194-0092
authors.initials: JM
authors.lastname: Clark
authors.forename: Thomas A
authors.identifier: http://orcid.org/0000-0002-3592-6386
authors.initials: TA
authors.lastname: Louis
authors.forename: Lawrence J
authors.identifier: http://orcid.org/0000-0002-0673-6823
authors.initials: LJ
authors.lastname: Appel
mesh_terms: D000328:Adult; D001835:Body Weight; D005260:Female; D006801:Humans; D020407:Internet; D008297:Male; D009765:Obesity / Q000628:therapy; D012307:Risk Factors; D057566:Self Report; D015431:Weight Loss; D061217:Weight Reduction Programs
keywords: Internet; obesity; self-report; weight loss