in blood oxygen levels. The accuracy of pulse oximetry deteriorates considerably for readings below 80%. Research has suggested that error rates in common pulse oximeter devices may be higher for adults with dark skin color, leading to claims of encoding systemic racism in countries with multi-racial populations such as the United States. Studies indicate that while accuracy with dark skin is good at higher, healthy saturation levels, some devices overestimate the saturation at lower levels, which may lead to hypoxia not being detected. A study that reviewed thousands of cases of occult hypoxemia, where patients were found to have oxygen saturation below 88% per arterial blood gas measurements despite pulse oximeter readings indicating 92% to 96% oxygen saturation, found that Black patients were three times as likely as White patients to have their low oxygen saturation missed by pulse oximeters. Further studies and computer simulations show that the increased amounts of melanin found in people with darker skin scatters the photons of light used by the pulse oximeters, decreasing the accuracy of the measurements; as the studies used to calibrate the devices typically oversample people with lighter skin, the parameters for pulse oximeters are set based on information that is not equitably balanced to account for diverse skin colors. This inaccuracy can lead to potentially missing people who need treatment, as pulse oximetry is used for the screening of sleep apnea and other types of sleep-disordered breathing which in the United States are conditions more prevalent among minorities. Equipment Consumer pulse oximeters In addition to pulse oximeters for professional use, many inexpensive "consumer" models are available. Opinions vary about the reliability of consumer oximeters; a typical comment is "The research data on home monitors has been mixed, but they tend to be accurate within a few percentage points". Some smart watches with activity tracking incorporate an oximeter function. An article on such devices, in the context of diagnosing COVID-19 infection, quoted João Paulo Cunha of the University of Porto, Portugal: "these sensors are not precise, that's the main limitation ... the ones that you wear are only for the consumer level, not for the clinical level". Pulse oximeters used for diagnosis of conditions such as COVID-19 should be Class IIB medical grade oximeters. Class IIB oximeters can be used on patients of all skin colors, low pigmentation and in the presence of motion. When a pulse oximeter is shared between