+ Reply to Thread
Results 1 to 9 of 9

Thread: Interpretation of 99% confidence interval

  1. #1
    Points: 16, Level: 1
    Level completed: 31%, Points required for next Level: 34

    Posts
    5
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Interpretation of 99% confidence interval




    Hello guys,

    this is my first post here in the forum and if I missed anything, then pls correct me.

    My first statistic class starts this week but I have already to do some homework before the first class.

    One task is the calculation and interpretation of a 99% confidence intervall.

    The task was the fallowing: 79% of the Democrats are in favor of Hillary Clition for presendency. Total people asked: 649. Construct a 99% CI interval for the proportion Democrats in favor of Hillary Clinton.

    My calculation so far:

    n = 649

    p̂ = 79:649 = 0.122

    p̂ Z √ p̂ (1- p̂): n

    0.122 (2.567) √ 0.122 (1-0.122): 649

    0.122 + (2.567) √ 0.122 (1-0.122): 649 = 0.155

    0.122 - (2.567) √ 0.122 (1-0.122): 649 = 0.89

    = (0.155, 0.89)

    But now I am stucked with the interpretation of the CI, even I read all chapters of my book it isn't clear to me.

    It would be nice if someone could helping me with the interpretation.


    Greetings
    7thSlap

  2. #2
    Devorador de queso
    Points: 95,540, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Awards:
    Posting AwardCommunity AwardDiscussion EnderFrequent Poster
    Dason's Avatar
    Location
    Tampa, FL
    Posts
    12,930
    Thanks
    307
    Thanked 2,629 Times in 2,245 Posts

    Re: Interpretation of 99% confidence interval

    You have quite a few issues here. Although my first question is who is assigning you to create and interpret confidence intervals BEFORE you have your first stats class? That's crazy talk.

    The second is that you're misunderstanding how to get \hat{p}. It's number of successes over the total sample size. In this case you don't have the number of successes - you were given \hat{p} = .79 directly.

    The third issue is that when it came time to calculate the end points you didn't do the computation correctly. I'm not going to dig through and figure out exactly what error your made since the p-hat wasn't correct anyways.
    I don't have emotions and sometimes that makes me very sad.

  3. #3
    Points: 16, Level: 1
    Level completed: 31%, Points required for next Level: 34

    Posts
    5
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Re: Interpretation of 99% confidence interval

    Hi, thanks for answering.

    My problem is that I missed my statistic course of the last year. I assumed I could repeat this course, but now the course isn't offered anymore. My professor enrolled me instead for the "statistics II" course of the fallowing year. So the professor assume that the students know the content of the first year, but I don't. I just got the homework a few days ago and the first lecture is this week...

    Could you tell me how to calculate p-hat correctly?

  4. #4
    Devorador de queso
    Points: 95,540, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Awards:
    Posting AwardCommunity AwardDiscussion EnderFrequent Poster
    Dason's Avatar
    Location
    Tampa, FL
    Posts
    12,930
    Thanks
    307
    Thanked 2,629 Times in 2,245 Posts

    Re: Interpretation of 99% confidence interval

    Quote Originally Posted by Dason View Post
    you were given \hat{p} = .79 directly.
    \hspace{.1cm}
    I don't have emotions and sometimes that makes me very sad.

  5. #5
    Points: 16, Level: 1
    Level completed: 31%, Points required for next Level: 34

    Posts
    5
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Re: Interpretation of 99% confidence interval

    Quote Originally Posted by Dason View Post
    \hspace{.1cm}
    Oh sorry, I am blind. I did the calculation again, is it right now?

    p̂ = 0.79
    p̂ Z √ p̂ (1- p̂): n

    0.79 (2.567) √ 0.79 (1-0.79): 649

    0. 0.79 + (2.567) √ 0. 0.79 (1-0.79): 649 = 0.83

    0.79 - (2.567) √ 0. 0.79 (1-0.79): 649 = 0 .75

    = (0.83, 0.75)

  6. #6
    Devorador de queso
    Points: 95,540, Level: 100
    Level completed: 0%, Points required for next Level: 0
    Awards:
    Posting AwardCommunity AwardDiscussion EnderFrequent Poster
    Dason's Avatar
    Location
    Tampa, FL
    Posts
    12,930
    Thanks
    307
    Thanked 2,629 Times in 2,245 Posts

    Re: Interpretation of 99% confidence interval

    I would flip the limits around since usually we do (lower_boundary, upper_boundary) so use (.75, .83) instead. But that looks good.
    I don't have emotions and sometimes that makes me very sad.

  7. #7
    Points: 16, Level: 1
    Level completed: 31%, Points required for next Level: 34

    Posts
    5
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Re: Interpretation of 99% confidence interval

    Ok, thanks a lot! Now back to my initially problem: How do I interpretate the confidence interval?

  8. #8
    Points: 1,821, Level: 25
    Level completed: 21%, Points required for next Level: 79
    Buckeye's Avatar
    Location
    Ohio
    Posts
    102
    Thanks
    31
    Thanked 4 Times in 4 Posts

    Re: Interpretation of 99% confidence interval

    If you repeat the experiment a number of times, 99% of the intervals will contain the proportion. Are you sure you don't want to take Stat 1? Do you know the material from Stat 1?
    "I have discovered a truly remarkable proof of this theorem which this margin is too narrow to contain." Pierre de Fermat

  9. #9
    Points: 16, Level: 1
    Level completed: 31%, Points required for next Level: 34

    Posts
    5
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Re: Interpretation of 99% confidence interval


    Thank you. I would like to take Stat 1, but then I have to wait more than 6 months before the course is offered again. I will read the chapters of Stat 1 and maybe get some private stat lesseons.

+ Reply to Thread

           




Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts






Advertise on Talk Stats