Question

Safety is critical in your plant of 1200 hundred employees. The average lost time accidents per month historically is 3. A six sigma team has been assigned to reduce this frequency. After a lengthy project, they identified the largest cause was arm burns in the Heat treat area. A series of countermeasures were implemented. The next month, the lost time accidents were zero. What is your conclusion after this month (assume Poisson)?

Answer 1

We want to test null hypothesis, H0 : = 0 against H1: 0

Let = 3, = 3 .... mean and variance of Poisson distribution both equal to 3

n= 1200 ... (n>30) use Z test.. large sample test

Test statistic,

      Z=

     Z=

    Z =

Z= 60

Calculate value=Z = 60

Consider = 5% level of significance

Table value = = 1.96

Decision Rule = Z > , Reject H0 at 5% level of significance.

Conclusion : It is insufficient evidence that the next month, the lost time accidents were zero.