
 Statistics Glossary  random variables and probability distributions 
  The (population) variance of a random variable is a nonnegative number which gives an idea of how widely spread the values of the random variable are likely to be; the larger the variance, the more scattered the observations on average. 
  Examples of discrete random variables include the number of children in a family, the Friday night attendance at a cinema, the number of patients in a doctor's surgery, the number of defective light bulbs in a box of ten. 
  Typically, a Geometric random variable is the number of trials required to obtain the first failure, for example, the number of tosses of a coin untill the first 'tail' is obtained, or a process where components from a production line are tested, in turn, until the first defective item is found. 
 www.stats.gla.ac.uk /steps/glossary/probability_distributions.html (2101 words) 
