A little help with simple stats ...

[Hong A Ng]

Hi everyone,

I am going through some practice questions from a study guide and have the answers; however I can't seem to figure out why the answer is that way. My mind just isn't wrapping around it. Would someone be able to provide me with some pointers?

q#1 

Your company focuses on individuals with a minimum of $100K in investments (about one million), though it offers more comprehensive services to those with over $500K and over $1 million. It is especially interested in data on those segments. It knows that individuals with $500K to $1 million in investments represent 20% of its market, while those with over $1 million in investments represent only 5%. Your marketing team wants information that is as accurate as possible. You have budget enough to complete 600 surveys. Would a disproportionate sample be the right choice for this survey? Why or why not? Would a disproportionate sample affect the overall reliability of the data on the population? What would the confidence interval at the 95% confidence level be for the population if 200 interviews were conducted with:
 

•   individuals with > $100K to < $500K in investments;
  
•   individuals with $500K to $1million in investments; and
  
•   individuals with > $1million in investments. 
  

Below is the answer; however I do not know where they came up with the 266 (I am assuming it's due to the disproportionate sample):

•   Since this is the equivalent of a sample size of 266, the confidence interval at the 95%
  confidence level would be +/-6 for the population 
  

q#2

0. 0. 
      What is the confidence interval at the 95% confidence level for Region 1 with a sample of 260 and for all Regions if the sample is 600? 
      

   Below is the answer, however I am not sure where they got the formulation (SQRT(2500 etc). Could someone exlapin?

   
   

   •   The confidence interval for Region 1 for a sample of 260 is approximately +/-6.1%
     SQRT(2500/260)*1.96
     
   •   The confidence interval for all regions based on a sample of 600 is
     approximately +/-4% (SQRT(2500/600)*1.96) 
     

Thank you so much friends!

0. 
   

[David Marso]

Hong,
  Please start a NEW topic rather than posting under someone else's topic!
Please delete this post and start anew!
The Management
---

Hong A Ng wrote

Hi everyone,
I am going through some practice questions from a study guide and have the answers; however I can't seem to figure out why the answer is that way. My mind just isn't wrapping around it. Would someone be able to provide me with some pointers?
q#1
               
       
       
               
                        Your company focuses on individuals with a
minimum of $100K in investments (about one million), though it offers more
comprehensive services to those with over $500K and over $1 million. It is especially
interested in data on those segments. It knows that individuals with $500K to $1 million
in investments represent 20% of its market, while those with over $1 million in
investments represent only 5%. Your marketing team wants information that is as accurate as possible.
You have budget enough to complete 600 surveys. Would a disproportionate sample be the right choice for this survey? Why or why not?
Would a disproportionate sample affect the overall reliability of the data on the
population? What would the confidence interval at the 95% confidence level be for the
population if 200 interviews were conducted with:

               
       
       
                 


                       
                               
                                          individuals with > $100K to < $500K in investments;


                               
                               
                                          individuals with $500K to $1million in investments; and


                               
                               
                                          individuals with > $1million in investments.

                               
                       
Below is the answer; however I do not know where they came up with the 266 (I am assuming it's due to the disproportionate sample):

               
       
       
               
                       
                               
                                          Since this is the equivalent of a sample size of 266, the confidence interval at the 95%


                                        confidence level would be +/-6 for the population

                               
                       
q#2
               
       
       
               
                       
                               
                                       
                                               
                                                       
                       
                               
                                       
                                               
                                                       
               
       
       
               
What is the confidence interval at the 95% confidence level for Region 1 with a sample of 260 and for all Regions if the sample is 600?
Below is the answer, however I am not sure where they got the formulation (SQRT(2500 etc). Could someone exlapin?

               
       
       
               
                       
                               
                                          The confidence interval for Region 1 for a sample of 260 is approximately +/-6.1%


                                        SQRT(2500/260)*1.96


                               
                               
                                          The confidence interval for all regions based on a sample of 600 is


                                        approximately +/-4% (SQRT(2500/600)*1.96)

                               
                       
               
                               
                       
               
Thank you so much friends!

[Bruce Weaver]

Just a few observations!

1. Posting under another topic and changing the subject line does result in a new thread in the UGA archive (see http://listserv.uga.edu/cgi-bin/wa?A1=ind1401&L=spssx-l), but not in the Nabble archive.

2. I believe that Hong can delete the original post only if it was posted via Nabble, and then it will be deleted only in the Nabble archive.

3. If he reposts in Nabble as a new topic, it will appear for a second time in the UGA archive (and in the inboxes of those who participate via e-mail).  

In light of all that, I think a better solution would be for one of the administrators of the Nabble archive to move the thread starting with Hong's post to a new topic.  This solves the problem of it being buried in another thread in Nabble, and does not cause it to appear twice in the UGA archive or in people's inboxes.  

My tuppence, FWIW!

David Marso wrote

Hong,
  Please start a NEW topic rather than posting under someone else's topic!
Please delete this post and start anew!
The Management
---

Hong A Ng wrote

Hi everyone,
I am going through some practice questions from a study guide and have the answers; however I can't seem to figure out why the answer is that way. My mind just isn't wrapping around it. Would someone be able to provide me with some pointers?
q#1
               
       
       
               
                        Your company focuses on individuals with a
minimum of $100K in investments (about one million), though it offers more
comprehensive services to those with over $500K and over $1 million. It is especially
interested in data on those segments. It knows that individuals with $500K to $1 million
in investments represent 20% of its market, while those with over $1 million in
investments represent only 5%. Your marketing team wants information that is as accurate as possible.
You have budget enough to complete 600 surveys. Would a disproportionate sample be the right choice for this survey? Why or why not?
Would a disproportionate sample affect the overall reliability of the data on the
population? What would the confidence interval at the 95% confidence level be for the
population if 200 interviews were conducted with:

               
       
       
                 


                       
                               
                                          individuals with > $100K to < $500K in investments;


                               
                               
                                          individuals with $500K to $1million in investments; and


                               
                               
                                          individuals with > $1million in investments.

                               
                       
Below is the answer; however I do not know where they came up with the 266 (I am assuming it's due to the disproportionate sample):

               
       
       
               
                       
                               
                                          Since this is the equivalent of a sample size of 266, the confidence interval at the 95%


                                        confidence level would be +/-6 for the population

                               
                       
q#2
               
       
       
               
                       
                               
                                       
                                               
                                                       
                       
                               
                                       
                                               
                                                       
               
       
       
               
What is the confidence interval at the 95% confidence level for Region 1 with a sample of 260 and for all Regions if the sample is 600?
Below is the answer, however I am not sure where they got the formulation (SQRT(2500 etc). Could someone exlapin?

               
       
       
               
                       
                               
                                          The confidence interval for Region 1 for a sample of 260 is approximately +/-6.1%


                                        SQRT(2500/260)*1.96


                               
                               
                                          The confidence interval for all regions based on a sample of 600 is


                                        approximately +/-4% (SQRT(2500/600)*1.96)

                               
                       
               
                               
                       
               
Thank you so much friends!