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Title: Nature and extent of selection bias resulting from convenience sampling in the emergency department.
Austin Authors: Lines, Travis;Burdick, Christine;Dewez, Xanthea;Aldridge, Emogene;Neal-Williams, Tom;Walker, Kimberly;Akhlaghi, Hamed;Paul, Buntine;Taylor, David McD 
Affiliation: Department of Medicine, The University of Melbourne, Melbourne, Victoria, Australia
Northern Health, Epping, Victoria, Australia
Western Health, Footscray, Victoria, Australia, Footscray, Victoria, Australia
Department of Medicine, The University of Melbourne, Melbourne, Victoria, Australia
Department of Emergency Medicine, St Vincent's Hospital Melbourne Pty Ltd, Fitzroy, Victoria, Australia
Alfred Health, Prahran, Victoria, Australia
Emergency Medicine, Eastern Health, Melbourne, Victoria, Australia
Issue Date: Apr-2022
Date: 2021-10-27
Publication information: Emergency medicine journal : EMJ 2022; 39(4): 325-330
Abstract: To compare the clinical and demographic variables of patients who present to the ED at different times of the day in order to determine the nature and extent of potential selection bias inherent in convenience sampling METHODS: We undertook a retrospective, observational study of data routinely collected in five EDs in 2019. Adult patients (aged ≥18 years) who presented with abdominal or chest pain, headache or dyspnoea were enrolled. For each patient group, the discharge diagnoses (primary outcome) of patients who presented during the day (08:00-15:59), evening (16:00-23:59), and night (00:00-07:59) were compared. Demographics, triage category and pain score, and initial vital signs were also compared. 2500 patients were enrolled in each of the four patient groups. For patients with abdominal pain, the diagnoses differed significantly across the time periods (p<0.001) with greater proportions of unspecified/unknown cause diagnoses in the evening (47.4%) compared with the morning (41.7%). For patients with chest pain, heart rate differed (p<0.001) with a mean rate higher in the evening (80 beats/minute) than at night (76). For patients with headache, mean patient age differed (p=0.004) with a greater age in the daytime (46 years) than the evening (41). For patients with dyspnoea, discharge diagnoses differed (p<0.001). Asthma diagnoses were more common at night (12.6%) than during the daytime (7.5%). For patients with dyspnoea, there were also differences in gender distribution (p=0.003), age (p<0.001) and respiratory rates (p=0.003) across the time periods. For each patient group, the departure status differed across the time periods (p<0.001). Patients with abdominal or chest pain, headache or dyspnoea differ in a range of clinical and demographic variables depending upon their time of presentation. These differences may potentially introduce selection bias impacting upon the internal validity of a study if convenience sampling of patients is undertaken.
DOI: 10.1136/emermed-2021-211390
ORCID: 0000-0002-8986-9997
Journal: Emergency Medicine Journal : EMJ
PubMed URL: 34706898
Type: Journal Article
Subjects: emergency department
Appears in Collections:Journal articles

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