Participants, consent and approval of study

A total of 186 nursing home residents from seven nursing homes in Denmark were enrolled in the study. In Denmark, the average age when moving into a nursing home is 83.7 years, and approximately 42% of nursing home residents are diagnosed with dementia, but the precise prevalence of dementia is unknown [27]. Written informed consent was obtained from all participants or their relatives. The participants could withdraw from the study at any point. Inclusion criteria were that the participants were able to sit up during visits. Exclusion criteria were allergic reactions or fear of dogs. None of the residents had pets of their own, but in a few cases the nursing homes had a resident cat. The study was approved by The Scientific Ethical Committee for Denmark. The clinical trial was not registered before conducting the study, as we were not aware that this was the general practice for this type of study. However, the study is now registered, with the registry name “Optimal Dog visits” and the ID number “{"type":"clinical-trial","attrs":{"text":"NCT04635124","term_id":"NCT04635124"}}NCT04635124” (https://clinicaltrials.gov/ct2/show/{"type":"clinical-trial","attrs":{"text":"NCT04635124","term_id":"NCT04635124"}}NCT04635124). Data were collected from August 2015 to October 2017. Fig 1 shows the CONSORT flowchart.