title: A tale of two models: Changes in psychological need satisfaction and physical activity over 3 years.
abstract: OBJECTIVE
  (a) Examine longitudinal measurement invariance of scores from psychological need satisfaction (PNS) scales, and (b) examine if changes in PNS were associated with change in moderate-to-vigorous physical activity (MVPA).
  
  
  METHODS
  Adolescents (N = 842, Mage = 10.8, SD = .6) enrolled in the Monitoring Activities of Teenagers to Comprehend their Habits (MATCH) study completed measures of PNS and MVPA every 4 months over a 3-year period (2011-14) for a total of 9 times.
  
  
  RESULTS
  PNS scores demonstrated strong longitudinal measurement invariance (i.e., invariant factor loadings and intercepts). Latent growth curve modeling indicated that a factor representing perceptions of all 3 PNS variables was positively associated with MVPA at Time 1 (β = .562, p < .05), and that increases in the common PNS factor were associated with increases in MVPA (β = .545, p < .05) with a large effect size (Rinitial MVPA2 = .316; Rchange in MVPA2 = .301). In an alternative model, MVPA at Time 1 was associated with perceived common PNS at Time 1 (β = .602, p < .001), and increases in MVPA were associated with increases in common PNS (β = .667, p < .001) with a large effect size (Rinitial PNS2 = .363 of the Rchange in PNS2 = .426).
  
  
  CONCLUSIONS
  Longitudinal measurement invariance was supported, and therefore PNS scores could be used to study change over time. Further, 2 equally well fitting models were found suggesting that change in PNS can be both an antecedent and an outcome of MVPA. As such, both PNS and MVPA could be targeted in interventions aimed at increasing need satisfaction or MVPA.
authors.affiliation: Healthy Active Living and Obesity Research Group, Children's Hospital of Eastern Ontario.
authors.forename: Katie E
authors.initials: KE
authors.lastname: Gunnell
authors.affiliation: Department of Family Medicine, Université de Sherbrooke.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Bélanger
authors.affiliation: School of Human Kinetics, University of Ottawa.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Brunet
mesh_terms: D000293:Adolescent; D002648:Child; D005260:Female; D006184:Habits; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008960:Models, Psychological; D009043:Motor Activity; D010549:Personal Satisfaction; D011582:Psychological Theory