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.
Selection Bias Selection bias is defined as a bias when the subjects, groups or data is selected for the analysis is not randomly selected and forms a non representative sample of the given population. In other words, selection bias occurs where there is no randomization while selecting a sample and thus the selected sample is not a representative sample for the population. It is also known as selection effect. Some of the examples of selection bias are given below: