Introduction. The standard deviation is a measure of the spread of scores within a set of data. Usually, we are interested in the standard deviation of a population. However, as we are often presented with data from a sample only, we can estimate the population standard deviation from a sample standard deviation.ntroduction. The standard deviation is a measure of the spread of scores within a set of data. Usually, we are interested in the standard deviation of a population. However, as we are often presented with data from a sample only, we can estimate the population standard deviation from a sample standard deviation.
Itching usually results from dry skin, a skin disorder, or an allergic reaction. If the person has no rash or skin abnormalities, the cause may be a drug, an allergic reaction that has internal effects, or a systemic disorder.
1 Dry skin. 2  Most itchy skin without visible rash is caused by dry skin. 3  Having a dry skin may be obvious through flaked, scaled and peeled skin. 4  Dry skin can be caused by cold weather and lack of moisturizing. 5  Scabies infection. 6  Scabies is caused by a microscopic organism, Sarcoptes scabiei.