title: Changes in quality of life from a homelessness intervention: true change, response shift, or random variation.
abstract: Participants experiencing homelessness and mental illness who received housing and support through the At Home/Chez Soi trial showed modest gains in quality of life (QOL) compared to treatment as usual participants. Participants' QOL ratings over time may have been affected by either response shift triggered by new life circumstances or by random variation in the meaning of QOL ratings. This study seeks to identify both phenomena to estimate the intervention's effect on true change in QOL.
  
  
  
  Using the residuals from a regression model of the global item of Lehman's 20-item quality of life interview (QOLI-20), latent trajectory analysis was used to identify response shift, while a measure of overall variability in residuals identified random variation of QOL. The latter was used to adjust group comparisons of QOLI-20 total scores and the global item.
  
  
  
  Equivalent distributions of both groups' participants across latent trajectory classes (χ2= 2.97, p = .397) suggest that the intervention did not trigger response shift. However, random variation interacted significantly with the treatment effect on global item ratings. For every increase of one standard deviation of residuals, treatment odds ratios decreased by a factor of 0.70 (SE 1.18, p = .036, 95% CI 0.50-0.98).
  
  
  
  Measuring random variation in QOL ratings from the standard deviation of residuals offers the ability to approximate, although indirectly, how participants' QOL is truly affected by a housing intervention. Specifically, we found that QOL improvement is more evident when QOL ratings have a consistent meaning over time.
authors.affiliation: Department of Epidemiology, McGill University, Montreal, Canada. guido.powell@mail.mcgill.ca.
authors.forename: Guido Antonio
authors.initials: GA
authors.lastname: Powell
authors.affiliation: Departments of Psychiatry and Community Health Sciences, University of Calgary, Calgary, Canada.
authors.forename: Carol E
authors.initials: CE
authors.lastname: Adair
authors.affiliation: Department of Psychiatry and Behavioural Neurosciences, McMaster University, Hamilton, Canada.
authors.forename: David L
authors.initials: DL
authors.lastname: Streiner
authors.affiliation: Department of Epidemiology, McGill University, Montreal, Canada.|Center for Outcomes Research and Evaluation (CORE), Research Institute of McGill University Health Center, Montreal, Canada.
authors.forename: Nancy
authors.initials: N
authors.lastname: Mayo
authors.affiliation: Douglas Institute Research Centre, McGill University, Montreal, Canada.|Department of Psychiatry, McGill University, Montreal, Canada.
authors.forename: Eric
authors.initials: E
authors.lastname: Latimer
mesh_terms: D000328:Adult; D005260:Female; D006703:Ill-Housed Persons / Q000523:psychology*; D006801:Humans; D008297:Male; D011788:Quality of Life / Q000523:psychology*
keywords: Homelessness; Mental illness; Quality of life appraisal; Response shift