title: Equating scores of the University of Pennsylvania Smell Identification Test and Sniffin' Sticks test in patients with Parkinson's disease.
abstract: Impaired olfaction is an important feature in Parkinson's disease (PD) and other neurological diseases. A variety of smell identification tests exist such as "Sniffin' Sticks" and the University of Pennsylvania Smell Identification Test (UPSIT). An important part of research is being able to replicate findings or combining studies in a meta-analysis. This is difficult if olfaction has been measured using different metrics. We present conversion methods between the: UPSIT, Sniffin' 16, and Brief-SIT (B-SIT); and Sniffin' 12 and Sniffin' 16 odour identification tests.
  
  
  
  We used two incident cohorts of patients with PD who were tested with either the Sniffin' 16 (n = 1131) or UPSIT (n = 980) and a validation dataset of 128 individuals who took both tests. We used the equipercentile and Item Response Theory (IRT) methods to equate the olfaction scales.
  
  
  
  The equipercentile conversion suggested some bias between UPSIT and Sniffin' 16 tests across the two groups. The IRT method shows very good characteristics between the true and converted Sniffin' 16 (delta mean = 0.14, median = 0) based on UPSIT. The equipercentile conversion between the Sniffin' 12 and 16 item worked well (delta mean = 0.01, median = 0). The UPSIT to B-SIT conversion showed evidence of bias but amongst PD cases worked well (mean delta = -0.08, median = 0).
  
  
  
  We have demonstrated that one can convert UPSIT to B-SIT or Sniffin' 16, and Sniffin' 12 to 16 scores in a valid way. This can facilitate direct comparison between tests aiding future collaborative analyses and evidence synthesis.
authors.affiliation: School of Social and Community Medicine, University of Bristol, United Kingdom. Electronic address: Michael.Lawton@bristol.ac.uk.
authors.forename: Michael
authors.initials: M
authors.lastname: Lawton
authors.affiliation: Nuffield Department of Clinical Neurosciences, Division of Clinical Neurology, University of Oxford, United Kingdom; Oxford Parkinson's Disease Centre, University of Oxford, United Kingdom.
authors.forename: Michele T M
authors.initials: MT
authors.lastname: Hu
authors.affiliation: Nuffield Department of Clinical Neurosciences, Division of Clinical Neurology, University of Oxford, United Kingdom; Oxford Parkinson's Disease Centre, University of Oxford, United Kingdom.
authors.forename: Fahd
authors.initials: F
authors.lastname: Baig
authors.affiliation: Nuffield Department of Clinical Neurosciences, Division of Clinical Neurology, University of Oxford, United Kingdom; Oxford Parkinson's Disease Centre, University of Oxford, United Kingdom.
authors.forename: Claudio
authors.initials: C
authors.lastname: Ruffmann
authors.affiliation: Department of Neurology, Institute of Neurological Sciences, Queen Elizabeth University Hospital, Glasgow, United Kingdom.
authors.forename: Eilidh
authors.initials: E
authors.lastname: Barron
authors.affiliation: Department of Neurology, Institute of Neurological Sciences, Queen Elizabeth University Hospital, Glasgow, United Kingdom.
authors.forename: Diane M A
authors.initials: DM
authors.lastname: Swallow
authors.affiliation: Department of Neurology, Institute of Neurological Sciences, Queen Elizabeth University Hospital, Glasgow, United Kingdom.
authors.forename: Naveed
authors.initials: N
authors.lastname: Malek
authors.affiliation: Department of Neurology, Institute of Neurological Sciences, Queen Elizabeth University Hospital, Glasgow, United Kingdom.
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Grosset
authors.affiliation: Department of Neurology, Queen's Medical Centre, Nottingham, United Kingdom.
authors.forename: Nin
authors.initials: N
authors.lastname: Bajaj
authors.affiliation: Clinical Neurosciences, John van Geest Centre for Brain Repair, Cambridge, United Kingdom.
authors.forename: Roger A
authors.initials: RA
authors.lastname: Barker
authors.affiliation: Institute of Psychological Medicine and Clinical Neurosciences, Cardiff University, United Kingdom.
authors.forename: Nigel
authors.initials: N
authors.lastname: Williams
authors.affiliation: Institute of Neuroscience, University of Newcastle, United Kingdom.
authors.forename: David J
authors.initials: DJ
authors.lastname: Burn
authors.affiliation: Sobell Department of Motor Neuroscience, UCL Institute of Neurology, United Kingdom.
authors.forename: Thomas
authors.initials: T
authors.lastname: Foltynie
authors.affiliation: Department of Clinical Neuroscience, UCL Institute of Neurology, United Kingdom.
authors.forename: Huw R
authors.initials: HR
authors.lastname: Morris
authors.affiliation: Department of Molecular Neuroscience, UCL Institute of Neurology, United Kingdom.
authors.forename: Nicholas W
authors.initials: NW
authors.lastname: Wood
authors.affiliation: School of Social and Community Medicine, University of Bristol, United Kingdom.
authors.forename: Margaret T
authors.initials: MT
authors.lastname: May
authors.affiliation: Department of Neurology, Institute of Neurological Sciences, Queen Elizabeth University Hospital, Glasgow, United Kingdom.
authors.forename: Donald G
authors.initials: DG
authors.lastname: Grosset
authors.affiliation: School of Social and Community Medicine, University of Bristol, United Kingdom.
authors.forename: Yoav
authors.initials: Y
authors.lastname: Ben-Shlomo
mesh_terms: D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D016009:Chi-Square Distribution; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009812:Odorants; D000857:Olfaction Disorders / Q000175:diagnosis* / Q000209:etiology*; D010300:Parkinson Disease / Q000150:complications*; D015203:Reproducibility of Results; D012684:Sensory Thresholds / Q000502:physiology; D012903:Smell / Q000502:physiology*
keywords: Equating; Item Response Theory; Olfaction; Sniffin’ Sticks; University of Pennsylvania Smell Identification Test