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.
Niacin is an important B vitamin found in animal foods like red meat, liver and fish. It's also found in some plant foods like beans, carrots and leafy green vegetables. Niacin helps protect against cardiovascular disease and it also supports cognitive function, the nervous system and the digestive tract, so it's important to get enough niacin into your daily diet.