Chi square equation: what is it, and why do we use it?

Χ =Σ

2

(O - E)

_______

2

E

In this graph, X^2 is our chi squared value. We find this by following the second part of the equation. When finding the chi squared value, we multiple Σ (the sum of the results of the six categories) by [O - E]^2 (the difference of the expected data and the observed data, both squared together) divided by the expected data (E). We then use this chi squared value to compare with the degrees of freedom chart.