title: Validity of Internet-based longitudinal study data: the elephant in the virtual room.
abstract: BACKGROUND
  Internet-based data collection relies on well-designed and validated questionnaires. The theory behind designing and validating questionnaires is well described, but few practical examples of how to approach validation are available in the literature.
  
  
  OBJECTIVE
  We aimed to validate data collected in an ongoing Internet-based longitudinal health study through direct visits to participants and recall of their health records. We demonstrate that despite extensive pre-planning, social desirability can still affect data in unexpected ways and that anticipation of poor quality data may be confounded by positive validation.
  
  
  METHODS
  Dogslife is a large-scale, Web-based longitudinal study of canine health, in which owners of Labrador Retrievers were recruited and questioned at regular intervals about the lifestyle and health of their dogs using an Internet-based questionnaire. The Dogslife questionnaire predominantly consists of closed-answer questions. In our work, two separate validation methodologies were used: (1) direct interviews with 43 participants during visits to their households and (2) comparison of owner-entered health reports with 139 historical health records.
  
  
  RESULTS
  Our results indicate that user-derived measures should not be regarded as a single category; instead, each measurement should be considered separately as each presents its own challenge to participants. We recommend trying to ascertain the extent of recall decay within a study and, if necessary, using this to guide data collection timepoints and analyses. Finally, we recommend that multiple methods of communication facilitate validation studies and aid cohort engagement.
  
  
  CONCLUSIONS
  Our study highlighted how the theory underpinning online questionnaire design and validation translates into practical data issues when applied to Internet-based studies. Validation should be regarded as an extension of questionnaire design, and that validation work should commence as soon as sufficient data are available. We believe that validation is a crucial step and hope our suggested guidelines will help facilitate validation of other Internet-based cohort studies.
authors.affiliation: The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Edinburgh, United Kingdom. Carys.Pugh@roslin.ed.ac.uk.
authors.forename: Carys A
authors.identifier: http://orcid.org/0000-0002-6548-0311
authors.initials: CA
authors.lastname: Pugh
authors.forename: Kim M
authors.identifier: http://orcid.org/0000-0002-7084-4386
authors.initials: KM
authors.lastname: Summers
authors.forename: B Mark C
authors.identifier: http://orcid.org/0000-0002-2541-6219
authors.initials: BM
authors.lastname: Bronsvoort
authors.forename: Ian G
authors.identifier: http://orcid.org/0000-0001-6407-4963
authors.initials: IG
authors.lastname: Handel
authors.forename: Dylan N
authors.identifier: http://orcid.org/0000-0002-0596-1885
authors.initials: DN
authors.lastname: Clements
mesh_terms: D000818:Animals; D003625:Data Collection / Q000592:standards*; D016208:Databases, Factual; D004285:Dogs; D005260:Female; D006801:Humans; D020407:Internet; D008137:Longitudinal Studies; D015203:Reproducibility of Results; D012107:Research Design; D011795:Surveys and Questionnaires / Q000592:standards
keywords: Internet; canine; epidemiology; health; longitudinal studies; questionnaires; validation studies as topic