Materials fatigue performance is commonly characterized by an "S-N curve", also known as a "Wöhler curve". This is often plotted with the cyclic stress ("S") against the cycles to failure ("N") on a logarithmic scale. S-N curves are derived from tests on samples of the material to be characterized (often called coupons or specimens) where a regular sinusoidal stress is applied by a testing machine which also counts the number of cycles to failure. This process is sometimes known as "coupon testing". For greater accuracy but lower generality component testing is used. Each coupon or component test generates a point on the plot though in some cases there is a "runout" where the time to failure exceeds that available for the test (see censoring). Analysis of fatigue data requires techniques from statistics, especially survival analysis and linear regression.