Question

Home Tools Tham Fropartics Ch-03.p:fx Sign In di Share P9.14. Stop sign obscrvancc studics are performed beforc and after an intensivc enforcement campaign. Results are summarized below. Use a contingency table to determine whether the difference in stop sign observance after the campaign was statistically significant at the 0.05 level of significance Before 62 30 20 112 After 58 20 l'otal 120 50 32 202 ED Stop Near stop No stop lotal 0 90 O Type hene so soarch 2:2019

Answer 1

For a Level of Significance in a contingency table is performed using chi-square test. So, based on that, the given values are considered as Observed Frequency.

Expected Frequency = ( Row Total X Column Total ) / N

Observed Frequency (Given Table)

	Before	After	Total
Stop	62	58	120
Near Stop	30	20	50
No Stop	20	12	32
Total	112	90	202

Expected Frequency

	Before	After
Stop	67	53
Near Stop	28	22
No Stop	18	14

Calculating ( O - E )²

	Before	After
Stop	25	25
Near Stop	4	4
No Stop	4	4

Calculating (O-E)² / E:

	Before	After
Stop	0.373134	0.471698
Near Stop	0.142857	0.181818
No Stop	0.222222	0.285714

Sum of (O-E)²/E =

1.677444

Degrees of Freedom = 6 -1 = 5

For a Degree of Freedom 5, chi value should be less than 11.7 for it significant upto 0.05.

So, 1.67 < 11.7. Hence, the answer is right! That the observance is statistically significant at 0.05 level of significance.