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 average cost of niobium is $25 to $30 per pound. Niobium or columbium is the chemical element with the symbol `Nbâ and the atomic number 41.A rare, soft, grey, ductile transition metal, niobium has physical and chemical properties similar to tantalum and the two are therefore difficult to distinguish.razil is the leading producer of niobium and ferroniobium, an alloy of niobium and iron. Niobium is mostly used in alloys and although alloys contain only a maximum of 0.1% of niobium, that small percentage is enough to improve the strength of the steel.