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Z score
A statistical score expressed in terms of its relative position in the frequency distribution of which it is a part. A score is converted to a z score so that it may be compared with scores from other tests or measuring instruments. A Z score is obtained by subtracting a raw score from the arithmetic mean of the distribution of scores and dividing by the standard deviation of the distribution. The Z score is often referred to as the standard score and occasionally as the sigma score.

Zipf migration hypothesis
An hypothesis in ecology proposed by George K Zipf that states that other factors such as income level, unemployment being equal, the number of persons who migrate between two communities (in both directions) will be equal to the product of the population of the two communities divided by the shortest distance between the communities. The hypothesis is often expressed in terms of the formula P1.P2/D in which P1 is the population of one community ,P2 the population of the other community and D the shortest distance between the two communities. It is sometimes referred to as the P1P2/D hypothesis and also the hypothesis on the intercity movement of persons and the minimum equation hypothesis.

Zone in tradition
The second of E.W Burgess five concentric zones: an area immediately surrounding the central business district of a large city that is being invaded by business and industrial expansion. Land value is high and expected to become higher when the are a eventually becomes part of the central business district. Because of this there is intense real estate speculation. Buildings are old and deteriorated and landlords who are often land speculators have little incentive to repair or improve them. This is the area of the slums and in Burgess' concentric zone hypothesis the existence of slums is explained primarily in terms of this process of transition in land use.

Zoning
The public regulation of land and building use in order to control the character of the community. Ideally areas of the city or town are restricted to specialized usage for the benefit of the public welfare of example, so that residential areas will not become interspersed with industry. Zoning is an aspect of community planning.