These magma plumes rise to the surface and form chains of volcanoes. Composite volcano magma contains more silica, SiO 2, than that of a shield volcano and is therefore stickier (more viscous). This stickiness plugs up the volcano, causing pressure to build-up. The result is an explosive, dangerous eruption.
It results in a biased sample, a non-random sample of a population (or non-human factors) in which all individuals, or instances, were not equally likely to have been selected. If this is not accounted for, results can be erroneously attributed to the phenomenon under study rather than to the method of sampling.
In statistics, bias refers to systematic error in the esti-. mation of a value. A biased test is one that systematically. overestimates or underestimates the value of the variable it. is intended to assess. If this bias occurs as a function of a. nominal cultural variable, such as ethnicity or gender, cul-.