z test

a type of statistical test that compares the means of two different samples to determine whether there is a significant difference between them (i.e., one not likely to have occurred by chance). Generally, this involves comparing the mean from a sample of a population to the mean for the whole population but may also involve comparing the means of two different populations. The z test is based on the normal distribution and is used when a population’s standard deviation is known or the sample is large (greater than 30). The equivalent t test is used with unknown standard deviations or smaller samples.

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Psychology term of the day

July 27th 2024

primary insomnia

in DSM–IV–TR, a sleep disorder characterized by difficulty in initiating or maintaining a restorative sleep to a degree in which the severity and persistence of the sleep disturbance causes clinically significant distress, impairment in a significant area of functioning, or both. The disorder is not caused by a general medical condition or the effects of a substance and is not exclusively an aspect of another sleep disorder or mental disorder. It is termed insomnia disorder in DSM–5. See dyssomnia. Compare primary hypersomnia.