Chi Square

Question

Vehicles heading west on Front Street may turn right, left, or go straight at Elm Street. The city traffic
engineer believes that half of the vehicles will turn left through the intersection. Of the remaining half, equal
proportions will go straight and turn right. Two hundred vehicles were observed, with the following results.
Using the 0.05 significance level, can we conclude that the traffic engineer is correct? (Use the P-Value Method)

 

                            Left Straight Right
Observed Frequency 90   60       50

 

I missed the lecture on it and having hard time trying to do it, 

 

Thank you for the help in advance

Answer 1

Hi Syed,

        The chi sq tests whether the observed frequency is statistically the same as the expected frequency or not. In this problem the expected frequency is 200*.5= 100 left turns, 50 straight and 50 right turns. The observed are 90 60 50

 

Next you calculate the chi sq statistic X=∑(Obs-Exp)/Exp from k=1 to 3 or use your TI calculator or Excel to calculate p from the chi sq distribution, I got p=.223

The nul H₀: there is no difference

            p>.05 so we fail to reject

Hope this helps

 

Jim