value. In contrast, deterministic health effects are radiation-induced effects such as acute radiation syndrome, which are caused by tissue damage. Deterministic effects reliably occur above a threshold dose and their severity increases with dose. Because of the inherent differences, LNT is not a model for deterministic effects, which are instead characterized by other types of dose-response relationships. LNT is a common model to calculate the probability of radiation-induced cancer both at high doses where epidemiology studies support its application, but controversially, also at low doses, which is a dose region that has a lower predictive statistical confidence. Nonetheless, regulatory bodies, such as the Nuclear Regulatory Commission (NRC), commonly use LNT as a basis for regulatory dose limits to protect against stochastic health effects, as found in many public health policies. Whether the LNT model describes the reality for small-dose exposures is disputed, and challenges to the LNT model used by NRC for setting radiation protection regulations were submitted. NRC rejected the petitions in 2021 because "they fail to present an adequate basis supporting the request to discontinue use of the LNT model". The LNT model opposes two competing schools of thought: the threshold model, which assumes that very small exposures are harmless, and the radiation hormesis model, which claims that radiation at very small doses can be beneficial. A 2016 peer-reviewed meta-analysis rejected the LNT on the basis of a lack of empirical evidence supporting it, and that it ignores biological effects, especially the self-correcting mechanisms in DNA which are effective up to a certain level of mutagenic agent. Because the current data is inconclusive, scientists disagree on which model should be used. Pending any definitive answer to these questions, the LNT model is applied through the precautionary principle. The model is sometimes used to quantify the cancerous effect of collective doses of low-level radioactive contaminations, which may produce estimates of excess deaths at levels that may have had zero deaths or saved lives in the two other models. Such practice has been criticized by the International Commission on Radiological Protection since 2007. The LNT model is sometimes applied to other cancer hazards such as polychlorinated biphenyls in drinking water. Origins The association of exposure to radiation with cancer had been observed as early as 1902, six years after the discovery of X-rays by Wilhelm Röntgen and radioactivity by Henri Becquerel. In 1927, Hermann Muller demonstrated that radiation may cause