The interrelation of several sizes during which leads changes of one to change of the others is called correlation. It is simple, multiple or partial. This concept is accepted not only in mathematics, but also in biology.
The word correlation came from the Latin word correlatio that the interrelation means. All phenomena, events and objects and also sizes characterizing them are connected among themselves. The correlation dependence differs from functional in the fact that in this type of dependence, consequences of any events can be measured only on average, approximately. The correlation dependence assumes that the variable corresponds to changes of independent size only with a certain degree of probability. Degree of dependence carries the name of coefficient of correlation. In biology the concept of correlation is a ratio of the building and functions of separate parts of an organism. Quite often correlation use a concept statistics. In the mute this relationship between statistical sizes, ranks and groups. For definition of existence or lack or existence of correlation use a special method. The method of correlation is applied to determination of direct or return overlapping in changes of numbers in ranks which compare. When the coefficient of correlation is found, measure a measure or degree of overlapping. But internal cause and effect factors are not found in such way. The main objective of statistics as sciences - to help to find such causal dependences to other sciences. In a form the correlation communication can be linear or nonlinear, positive and negative. When with increase or decrease of one of variables another also grows or decreases, the interrelation is linear. If at change of one size, the nature of changes another is not linear, then it is correlation is not linear. Positive the correlation is considered when increase in level of one size is followed by increase in level another. For example, when strengthening of a sound is followed by feeling of increase in its tone. The correlation when growth of level of one variable is followed by decrease in level another, is called negative. In communities of animals the increased level of uneasiness of an individual leads to the fact that the probability to occupy by this individual of the predominating niche among fellows decreases. When communication of variables is absent, the correlation carries names zero.