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.
The metal is used in arc-welding rods for some grades of stainless steel. It is used in advanced engineering systems such as those used in the Gemini space program. Some magnets contain niobium and superconductive magnets are made with Nb-Zr alloy wire.Because of its bluish colour, niobium is apparently being used for body art products, such as navel rings.t is used in advanced engineering systems such as those used in the Gemini space program. Some magnets contain niobium and superconductive magnets are made with Nb-Zr alloy wire. Because of its bluish colour, niobium is apparently being used for body art products, such as navel rings.