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 Allergic reactions may be accompanied by hives or rash. 2  Skin Conditions-Skin conditions such as eczema or sunburn can cause the body to become itchy all over as the body reacts to the condition. 3  Stress or anxiety may stimulate such conditions, leading to itching that is not localized to a particular area.