Survivorship curve

A survival curve is a graphical representation of the death rate (mortality) of a population over time. Survival curves are mainly used in biology and in clinical trials.

Description

On the ordinate (y-axis ) is typically the number of observed individuals is applied. In biology, a logarithmic ordinate classification of states is usually used. In clinical trials, usually a linear percentage scale. On the abscissa (x-axis ) the time is plotted. In most cases, with a linear scale. The data for a survival curve can be taken for example from a mortality table.

In biology, there are three fundamentally different types of survival curves:

Type I is characterized by a very low death rate for young and middle-aged individuals. Before reaching the area of the maximum life span, ie at an advanced age, the death rate then rises sharply. This type of survival curve is extremely rare in the wild. It is found in some species in captivity and modern humans in industrialized nations.
In type II, the mortality rate is equal at any age. This shape of the curve can be observed, for example, in many species of birds such as the white stork.
A very high mortality rate in low age distinguishes the type III. In middle and old age, however, it takes significantly. This curve can be observed in all living creatures with a very high number of offspring, such as frogs and dandelion. This is referred to organisms with an r- strategy (see: reproductive strategy ). This type of survival curve is most commonly found in nature.

These three types are idealized. Real survival curves they reach only approximately. Significant contributions to the survival curves of a number of animal species originate from the U.S. ecologist Edward Smith Deevey ( 1914-1988 ).

There are various modified forms of survival curves in clinical trials. One of them is, for example, the survival curve according to the Kaplan-Meier.

Survivorship curve

Description

Further Reading