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.
Uses. Niobium is used in alloys including stainless steel. It improves the strength of the alloys, particularly at low temperatures. Alloys containing niobium are used in jet engines and rockets, beams and girders for buildings and oil rigs, and oil and gas pipelines. This element also has superconducting properties.iobium is a useful metal in a range of specialist alloys. In amounts as low as 0.1 per cent it has a significant strengthening effect on steel, making it suitable for use in gas pipelines for example. It is also involved in some highly temperature-stable superalloys used for engine parts in the aerospace industry.