Stratified random sampling importance

The persons are selected on a stratified random sampling basis, with stratifications designated according to the type of exposure, quantity of exposure, degree of hazard present, and other criteria considered important to the representativeness of the sample. The objective is to discover causal factors that are critical, that is, that have contributed to an accident or potential accident situation. The unsafe acts and unsafe conditions identified by this method then serve as the basis for the identification of accident potential problem areas and the ultimate development of countermeasures designed to control accidents at the no-loss stage [p. 304],... 

While biochemical markers of bone metabolism may be sensitive to the effects of glucocorticoids in the short term, the relation between changes in these markers and intermediate measures, such as bone mineral density, and the more important clinical outcomes of fractures, is unknown. In a random stratified sample of 3222 women in the perimenopausal age range (47-56 years), including 119 women with asthma, bone mineral density was measured to determine whether asthma was a risk factor of osteoporosis and to investigate the effect of inhaled glucocorticoids (102). The subjects had predominantly adult-onset asthma, as the age at diagnosis was over 40 years. There were 26 patients who were treated mainly with... 

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