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.
This leads to bias. For example, suppose the study population includes multiple racial groups but members of one race participate less frequently in the type of study. A bias results. 2. Information bias (misclassification bias): Systematic error due to inaccurate measurement or classification of disease, exposure or other variables.