**Explain CORRELATION:** “The degree of relative correspondence, as between two sets of data.”[websters] If sales go up when the advertising budget goes up, they correlate. The correlation coefficient is a measure of how closely the two data sets correlate. A correlation coefficient of 1 is a perfect correlation, .9 is a strong correlation, and .2 is a weak correlation. This value can also be negative, as when the incidence of a disease goes down when vaccinations go up. A correlation coefficient of -1 is a perfect negative correlation. Always remember, though, that correlation does not imply causation. See also coefficient.

Different definitions in web development like **correlation** in Dictionary C.

- Manual Classification:
- Meaning of which of two or more categories an item falls under; a classic machine learning task. Deciding whether an email message is spam or not classifies it among two categories, and analysis of data correlation.
- Manual Continuous Variable:
- Meaning value can be any of an infinite number of values, typically within a particular range. For example, if you can express age or size with a decimal number, then they are continuous variables. In a correlation.
- Manual Coefficient:
- Meaning algebraic symbol prefixed as a multiplier to a variable or unknown quantity (Ex.: x in x(y + z), 6 in 6ab”[websters] When graphing an equation such as y = 3x + 4, the coefficient of x determines the correlation.
- Manual Cross-Validation:
- Meaning with an algorithm, “the name given to a set of techniques that divide up data into training sets and test sets. The training set is given to the algorithm, along with the correct answers... and correlation.
- Manual Chi-Square Test:
- Meaning like “pie” but beginning with a “k”) is a Greek letter, and chi-square is “a statistical method used to test whether the classification of data can be ascribed to chance or to some underlying law correlation.