The standard score of a raw score x is. where: The absolute value of z represents the distance between the raw score and the population mean in units of the standard deviation. z is negative when the raw score is below the mean, positive when above. A key point is that calculating z requires the population mean and the population standard deviation, not the sample mean or sample deviation.
The definition of a siren is a wailing sound made by passing air through a rotating disc, or a beautiful woman who uses sex to attract men, or a mythical female creature that lures men into the sea. 1  An example of a siren is the sound from a police car as it moves through traffic.
A civil defense siren (also known as an air-raid siren or tornado siren) is a siren used to provide emergency population warning of approaching danger and sometimes to indicate when the danger has passed.