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.
History and Uses: The story of niobium's discovery is a bit confusing. The first governor of Connecticut, John Winthrop the Younger, discovered a new mineral around 1734. He named the mineral columbite ((Fe, Mn, Mg)(Nb, Ta) 2 O 6) and sent a sample of it to the British Museum in London, England.uperconductive wire can be made from an alloy of niobium and titanium which can then be used to make superconductive magnets. Other alloys of niobium, such as those with tin and aluminum, are superconductive as well. Pure niobium is itself a superconductor when it is cooled below 9.25 K (-442.75Â°F).