Question

An extensive study conducted in 1980 concluded that the mean mercury level in oysters from the White Bear estuary was .021 ppm with a standard deviation of .031. in 2012 a sample of 41 oysters from the same estuary exhibited a mean mercury concentration of .007 ppm. Can you conclude that the 2012 mercury concentration is lower than in 1980? Use a=.01 level of significance. Use P-Value test.

Hypothesis with claim

TV

PV

Decision and explanation

Summary

Answer 1

Ho :   µ =   0.021      
Ha :   µ <   0.021 (claim) (Left tail test)

Level of Significance ,    α =    0.01                  
population std dev ,    σ =    0.0310                  
Sample Size ,   n =    41                  
Sample Mean,    x̅ =   0.0070                  
                          
'   '   '                  
                          
Standard Error , SE = σ/√n =   0.0310   / √    41   =   0.0048      
Z-test statistic= (x̅ - µ )/SE = (   0.007   -   0.021   ) /    0.005   =   -2.892
                          
  
p-Value   =   0.0019     [ Excel formula =NORMSDIST(z) ]              
Decision:   p-value<α, Reject null hypothesis                       
Conclusion: There is enough evidence to conclude that the 2012 mercury concentration is lower than in 1980 at α=0.01