How well do covariates perform when adjusting for sampling bias in online COVID-19 research? Insights from multiverse analyses

COVID-19 research has relied heavily on convenience-based samples, which-though often necessary-are susceptible to important sampling biases. We begin with a theoretical overview and introduction to the dynamics that underlie sampling bias. We then empirically examine sampling bias in online COVID-19 surveys and evaluate the degree to which common statistical adjustments for demographic covariates successfully attenuate such bias. This registered study analysed responses to identical questions from three convenience and three largely representative samples (total N = 13,731) collected online in Canada within the International COVID-19 Awareness and Responses Evaluation Study ( www.icarestudy.com ). We compared samples on 11 behavioural and psychological outcomes (e.g., adherence to COVID-19 prevention measures, vaccine intentions) across three time points and employed multiverse-style analyses to examine how 512 combinations of demographic covariates (e.g., sex, age, education, income, ethnicity) impacted sampling discrepancies on these outcomes. Significant discrepancies emerged between samples on 73% of outcomes. Participants in the convenience samples held more positive thoughts towards and engaged in more COVID-19 prevention behaviours. Covariates attenuated sampling differences in only 55% of cases and increased differences in 45%. No covariate performed reliably well. Our results suggest that online convenience samples may display more positive dispositions towards COVID-19 prevention behaviours being studied than would samples drawn using more representative means. Adjusting results for demographic covariates frequently increased rather than decreased bias, suggesting that researchers should be cautious when interpreting adjusted findings. Using multiverse-style analyses as extended sensitivity analyses is recommended.

Bilateral extensive vascular calcification of the breast associated with coagulative necrosis: a calciphylaxis-like syndrome

A case of asynchronous bilateral breast necrosis in a 40-year-old woman with untreated chronic hypercholesteraemia is described. Mastectomies were performed, and histological examination revealed bilateral breast calciphylaxis characterized by extensive vascular calcification with coagulative necrosis. Breast calciphylaxis is a rare disease clinically characterized by progressive tissular necrosis with secondary cutaneous ulceration and by vascular calcification and thrombosis. However, the nature of the vascular calcification has remained poorly understood up to now, owing to the absence of any precise mineralogical examination. In this case the mineral deposits were analysed for the first time: only hydroxyapatite was found. The etiology is discussed, and the high cholesterol rate of the patient is implicated.

Brushite in the pulp of primary molars

This study was undertaken to investigate the mineral phase of spherulitic calcifications discovered in the pulpous mesenchyme of human primary molars by microradiography. Analytical scanning electron microscopy and x-ray diffraction disclosed that well-crystallized brushite is the major compound of the spherulites. The mechanism leading to the crystallization of brushite is far from well understood. Histologically, on decalcified sections, inflammatory cells and capillaries can be seen trapped in the spherulites. In the light of these findings, it could be suggested that metabolic conditions may promote the crystallization of brushite in the pulp of primary molars.

Dental technician's pneumoconiosis. A report of two cases

Diagnosis of pneumoconiosis was made in 2 dental technicians presenting with interstitial lung disease. The occupational origin of inhaled dust was confirmed by mineralogic analyses, which disclosed mainly large amounts of chromium-cobalt-molybdenum particles originating from Vitallium prostheses, but also showed abrasives (silica and silicon carbide) and asbestos in 1 patient. The presence of Vitallium and its chemical stability in bronchoalveolar lavage and lung several years after cessation of exposure confirm the resistance of this alloy to corrosion by body fluids. This contrasts with the high solubility of cobalt described in cobalt or hard metal disease. We suggest that dental technician's pneumoconiosis is a complex pneumoconiosis distinct from silicosis, asbestosis, or hard metal disease and that Cr-Co-Mo alloys play a role in its pathogenesis.

Mineralogical analysis of bronchoalveolar lavage fluid as an aid to diagnosis of "imported" pleural asbestosis

Images

Asbestos bodies in bronchoalveolar lavage

Asbestos bodies (AB) were counted in bronchoalveolar lavage (BAL) fluid from 62 patients with suspected asbestos related diseases, 2 patients with known exposure to asbestos but without related disease, and 40 control subjects. BAL fluid contained AB in all patients with obvious exposure (28 of 28), including the 2 without related disease, in most patients with suspected exposure (26 of 28), as well as in 5 of 8 patients without known exposure but with suspicion of asbestos related disease (mesothelioma or pleural plaques). Among the 40 control subjects, the results in 5 were positive but to a low degree (less than 1 AB/ml of fluid). Quantitative analysis correlated with the type of disease: AB counts were higher in patients with interstitial lung disease than in those with benign (p less than 0.02) or malignant (p less than 0.01) pleural disease. Only 9 of 13 patients with mesothelioma had a positive lavage. In conclusion, the finding of AB in BAL fluid correlates with the occupational risk and can disclose unknown exposure better than a questionnaire, but a positive lavage is not a proof of disease. Quantitative differences in AB counts suggest a different pathogenesis for pleural and parenchymal disease.

[Primary hyperoxaluria. Clinical, histological and crystallographic study of the ocular lesions]

A post-mortem histological examination of the eyes of a case of primary hyperoxaluria revealed the presence of crystals in the ciliary processes and at the level of the retinal pigment epithelium. The crystallography study demonstrated that it consisted of wewhellite. The ocular lesions are compared with those found by other authors in primary hyperoxaluria, after prolonged methoxyflurane anaesthesia, after experimental administration of dibutyloxalic acid or naphthalene, and in the human retina in longstanding detachments. Most of the factors which give rise to the presence in the eye of oxalate and its selective precipitation in the midst of certain ocular tissues remain hypothetical. The retinal lesions observed in primary hyperoxaluria appear to be pathognomonic for hyperoxalaemia.

Search for Magnetite in Lunar Rocks and Fines

Magnetite crystals larger than 2 micrometers are absent from rocks and fines. Smaller opaque spheres in the fines can tentatively be identified as magnetite. Their concentration is not higher than 1 x 10(-6) particle per particle smaller than 1 millimeter. In the fines from the sampling site, the contribution of material similar to type 1 carbonaceous meteorites is insignificant, either because it never existed, or because it was evaporated or comminuted by impact or was diluted by indigenous material. Other magnetite habits typical of carbonaceous meteorites or possibly of cosmic dust or comets were also sought without success-such as rods, platelets, framboids, spherulites, and idiomorphic crystals.