In: Statistics and Probability
Television viewers often express doubts about the validity of certain commercials. In an attempt to answer their critics, a large advertiser wants to estimate the true proportion of consumers who believe what is shown in commercials. Preliminary studies indicate that about 40% of those surveyed believe what is shown in commercials. What is the minimum number of consumers that should be sampled by the advertiser to be 99% confident that their estimate will fall within 1% of the true population proportion?
sample proportion ,   p̂ =   
0.40          
           
   
sampling error ,    E =   0.01  
           
           
Confidence Level ,   CL=   0.99  
           
           
          
           
           
alpha =   1-CL =   0.01  
           
           
Z value =    Zα/2 =    2.576 [excel formula
=normsinv(α/2)]          
           
          
           
           
Sample Size,n = (Z / E)² * p̂ * (1-p̂) = (  
2.576   /   0.01   ) ² *  
0.40   * ( 1 -   0.40   ) =
   15923.75
          
           
           
          
           
           
so,Sample Size required=      
15924