X

(observed — expected)2 expected where 2 means the sum of all the squared differences between observed and expected divided by the expected values. To calculate the chi-square value for our black and gray kittens, we would first subtract the number of expected black kittens from the number of observed black kittens (30 — 37.5 = —7.5) and square this value: —7.52 = 56.25. We then divide this result by the expected number of black kittens, 56.25/37.5, = 1.5. We repeat the calculations on the number of expected gray kittens: (20 — 12.5)2/12.5 = 4.5. To obtain the overall chi-square value, we sum the (observed — expected)2/expected values: 1.5 + 4.5 = 6.0.

Table 3.4

Critical values of the x2 distribution

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