Its only advantage over the random sampling technique is simplicity. Systematic sampling is frequently used to select a specified number of records from a computer file. Stratified sampling is commonly used probability method that is superior to random sampling because it reduces sampling error. A stratum is a subset of the population that share at least one common characteristic. Examples of stratums might be males and females, or managers and non-managers.
| references | in Wikidata. Niobium, formerly columbium, is a chemical element with symbol Nb (formerly Cb) and atomic number 41. It is a soft, grey, ductile transition metal, which is often found in the pyrochlore mineral, the main commercial source for niobium, and columbite. Its name comes from Greek mythology, specifically Niobe, who was the daughter of Tantalus, the namesake of tantalum.
A large quantity of Niobium was discovered at Panda Hill in Mbeya Region in Tanzania. Two companies did the prospecting assessment; one of which is Rex Well, a subsidiary of Euronet Africa of UK. Mining could start any time. Last year's survey by the firm indicated that the area has about 90 million tonnes of Niobium. The company would use open cast method, as most of the mineral is found near the surface.