Statistical term describing the association of two variables in accordance with a significance measure

Correlation is a formal statistical test describing the relationship between two variables and at simplist is defined as either Peasons correlation statistic (r2) or Spearman's rank sign correlation (r). When the value is zero, the relationship between the variables is random, when it is +1 the relationship is perfectly inter-related such that if one variable changes the other will change inaccordance with this. If the correlation is -1 the relationship is adversely affected. Correlations of 0.7 are considered reasonably robust for r2 and 0.8 for r