# Thread: confidence interval

1. ## confidence interval

4) for over 20 years the occupational safety & health administration has required companies that handle hazardous chemicals to complete material safety data sheets (MSDSs) . These MSDSs have been criticized for being too hard to understand and complete by workers . Although improvements were implemented in 1990 , a more recent study of 150 MSDSs revealed that only 11% were satisfactorily completed ( chemical & Engineering news , Feb 7 , 2005 ).

a) give a point estimate of p , the true proportion of MSDSs that are satisfactorily completed.
b) Find a 95 % confidence interval for p
c) Give a practical interpretation of the interval , part b

2. Originally Posted by ekbio
a) give a point estimate of p , the true proportion of MSDSs that are satisfactorily completed.
$\displaystyle \hat{p} = \frac{x}{n}$

Originally Posted by ekbio
b) Find a 95 % confidence interval for p
$\displaystyle \displaystyle\hat{p}\pm Z_{\frac{\alpha}{2}}\times \sqrt{\frac{\hat{p}(1-\hat{p})}{n}}$

Originally Posted by ekbio
c) Give a practical interpretation of the interval , part b
The true proportion can be found in 95 out of 100 intervals constructed.