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anonymous

  • one year ago

Statistics/Probability questions... 1) How do I tell if the model accurately predicted the sales? 2) What is the "p" in this problem/what do I do with it? : "Assume p = 0.05" ___ I attached the full problem and a clearer version of what I think is called a 'Chi Squared Critical Values Chart.' ___ Could someone run me through how to do this problem?

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  1. anonymous
    • one year ago
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  2. LynFran
    • one year ago
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    you shd start by finding the degree of freedom do u know how to do that?

  3. anonymous
    • one year ago
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    No, I don't. I asked my proctor to help me, but he didn't know how either.

  4. LynFran
    • one year ago
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    ok there a formula for that (C-1)(R-1) where C represent the total # of column and R represent the total # of rows

  5. anonymous
    • one year ago
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    (12-1)(35-1)?

  6. LynFran
    • one year ago
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    no there 2 columns the expected and the observed ....and there 3 row.,vanilla, strawberry and chocolate

  7. LynFran
    • one year ago
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    correct now take away and then multiply out the brackets to get the df

  8. anonymous
    • one year ago
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    2

  9. LynFran
    • one year ago
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    correct the next step is to find the chi square value and there a formula for that also

  10. LynFran
    • one year ago
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    |dw:1435291295954:dw|

  11. LynFran
    • one year ago
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    so we plug in the respective values in the formula and add them up note: we do them separately i will start u will finish it ok

  12. anonymous
    • one year ago
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    Sounds good, thanks a bunch :)

  13. LynFran
    • one year ago
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    |dw:1435291759806:dw|

  14. anonymous
    • one year ago
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    6033 _____ ? 875

  15. anonymous
    • one year ago
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    ^(fraction)

  16. LynFran
    • one year ago
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    yes but we usually take the decimal in statistics

  17. LynFran
    • one year ago
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    which is 6.894857 now this is ur chi square value

  18. anonymous
    • one year ago
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    what now? is this where that "p" comes in?

  19. LynFran
    • one year ago
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    now the want the p value so we take the degree of freedom which is 2 and at p=0.05 which i dont see on this chi square tables??

  20. LynFran
    • one year ago
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    im seeing 0.005 on the table not 0.05

  21. LynFran
    • one year ago
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    and it there twice the table have a fault

  22. LynFran
    • one year ago
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    u see it? im assuming that the first 0.005 suppose to be 0.05??

  23. anonymous
    • one year ago
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    Maybe it is supposed to be the 5th column?

  24. LynFran
    • one year ago
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    no actually there shdnt have the same p value on a chi square table

  25. anonymous
    • one year ago
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    You're the expert; I'm in Algebra II. My proctor didn't know why it was included, and couldn't help me with it because he didn't know how to do stats either. There wasn't even a review or notes or anything, just questions. :/

  26. LynFran
    • one year ago
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    im lookin at my chi square table and well the p value for 0.05 corresponds to the first 0.005 on your chi sq. table so lets used that 0k

  27. anonymous
    • one year ago
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    Sure thing

  28. LynFran
    • one year ago
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  29. LynFran
    • one year ago
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    so |dw:1435293790254:dw|

  30. LynFran
    • one year ago
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    now we compare the 2 chi square value

  31. anonymous
    • one year ago
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    oh wait, so that was right? Because 6.83 > 5.99, the correct answer is either A or D?

  32. LynFran
    • one year ago
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    the answer shd be D because the p value was too low

  33. LynFran
    • one year ago
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    for the chi square

  34. anonymous
    • one year ago
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    Both A and D say x was too low

  35. LynFran
    • one year ago
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    ok u see what the difference between the two values?

  36. anonymous
    • one year ago
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    One says yes, and the other says no?

  37. anonymous
    • one year ago
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    referring to whether or not the model predicted the milkshake sales accurately

  38. anonymous
    • one year ago
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    but i don't know how to tell that from our data/if it should be yes or no

  39. LynFran
    • one year ago
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    and there a saying that goes like this....if the p-value is low H0 must go and if the p-value is high then h0 can fly

  40. LynFran
    • one year ago
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    ok the difference between the value is 0.84 can conclude D or A as the answer?

  41. anonymous
    • one year ago
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    I understand how to get 0.84 as the difference, but not how to tell if it is Yes or No

  42. LynFran
    • one year ago
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    https://www.youtube.com/watch?v=HwD7ekD5l0g

  43. LynFran
    • one year ago
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    ok what we actually had to look at is if p>0.05 or p<0.05

  44. anonymous
    • one year ago
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    I thought it said p=0.05 though?

  45. LynFran
    • one year ago
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    yes but when we find the value we see if its greater ok lesser than 0.05

  46. anonymous
    • one year ago
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    ..

  47. LynFran
    • one year ago
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    o no we were on the right track before i got mix up after watching that video that for critical value...so we do have to look at our 2 chi squared values to determine the answer

  48. anonymous
    • one year ago
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    okay. what about them?

  49. LynFran
    • one year ago
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    well the chi squared value is low and lets look at it this way the chi sq value doesnt equal our chi square value and once the chi squared values is too low then it says something about the test so i still think its D

  50. LynFran
    • one year ago
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    ok maybe if we get a second opionon an this it would be nice cause i really dont know how to explain the no it was to low part @SolomonZelman

  51. anonymous
    • one year ago
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    Thanks for all of your help so far @LynFran :)

  52. LynFran
    • one year ago
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    ok

  53. LynFran
    • one year ago
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    @jim_thompson5910

  54. jim_thompson5910
    • one year ago
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    LynFran you're using the right formula \[\Large \chi^2 = \sum \frac{(O_i -E_i)^2}{E_i}\] \[\Large \chi^2 = \frac{(O_1 -E_1)^2}{E_1}+\frac{(O_2 -E_2)^2}{E_2}+\frac{(O_3 -E_3)^2}{E_3}\] \[\Large \chi^2 = \frac{(205-175)^2}{175}+\frac{(114-125)^2}{125}+\frac{(264-250)^2}{250}\] \[\Large \chi^2 = 6.894857\]

  55. jim_thompson5910
    • one year ago
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    is there a typo in the table? I see 0.005 written twice along the top

  56. jim_thompson5910
    • one year ago
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    I'm guessing that first 0.005 should be 0.05 ?

  57. anonymous
    • one year ago
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    yes, there is

  58. jim_thompson5910
    • one year ago
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    ok thought so

  59. jim_thompson5910
    • one year ago
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    Degrees of Freedom df = k-1 = 3-1 = 2 look at the row that starts with 2 and look at the column that has 0.05 at the top

  60. jim_thompson5910
    • one year ago
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    So we know test statistic = 6.89 critical value = 5.99

  61. jim_thompson5910
    • one year ago
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    do you see how to finish up?

  62. LynFran
    • one year ago
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    actually we did all of this is just how to compare and tell the correct answer part that a bit troublesome

  63. jim_thompson5910
    • one year ago
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    Rule: if (test statistic) > (chi-square critical value), then reject the null

  64. jim_thompson5910
    • one year ago
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    the goodness of fit test is most always right tailed. I've never seen any cases that are otherwise, but I don't know for sure since there may be some rare cases

  65. anonymous
    • one year ago
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    @jim_thompson5910 okay, reject the null, but we can't determine whether it would be option A or D. (Yes, or No)

  66. anonymous
    • one year ago
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    from the options at the bottom of this attachment

  67. jim_thompson5910
    • one year ago
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    Null: the observed matches with the expected Alternate: the observed does not match with the expected we rejected the null, so the observed does not match with the expected The question was "did the model predict the sales correctly?" ie "does the expected and observed values match up?" so the the answer is "no". The reason why the null was rejected was because the chi-square test statistic was too high

  68. anonymous
    • one year ago
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    Ohhhh! so it's actually B I was looking at it backwards

  69. jim_thompson5910
    • one year ago
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    yeah it's B

  70. LynFran
    • one year ago
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    wasnt the chic squared values 5.99? so how come that higher than 6.89??

  71. anonymous
    • one year ago
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    Thank you both! I'll write your testimonials when I'm all done. (later tonight/early morning)

  72. jim_thompson5910
    • one year ago
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    that 5.99 is the critical value

  73. jim_thompson5910
    • one year ago
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    it's the cutoff point

  74. anonymous
    • one year ago
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    I greatly appreciate all the help :)

  75. jim_thompson5910
    • one year ago
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    anything higher than that cutoff point means you reject H0

  76. LynFran
    • one year ago
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    o ok i see

  77. jim_thompson5910
    • one year ago
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    |dw:1435292080595:dw|

  78. jim_thompson5910
    • one year ago
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    |dw:1435292122002:dw|

  79. LynFran
    • one year ago
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    yes ur right

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