anonymous
  • anonymous
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?
Statistics
  • Stacey Warren - Expert brainly.com
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jamiebookeater
  • jamiebookeater
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LynFran
  • LynFran
you shd start by finding the degree of freedom do u know how to do that?
anonymous
  • anonymous
No, I don't. I asked my proctor to help me, but he didn't know how either.

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LynFran
  • LynFran
ok there a formula for that (C-1)(R-1) where C represent the total # of column and R represent the total # of rows
anonymous
  • anonymous
(12-1)(35-1)?
LynFran
  • LynFran
no there 2 columns the expected and the observed ....and there 3 row.,vanilla, strawberry and chocolate
LynFran
  • LynFran
correct now take away and then multiply out the brackets to get the df
anonymous
  • anonymous
2
LynFran
  • LynFran
correct the next step is to find the chi square value and there a formula for that also
LynFran
  • LynFran
|dw:1435291295954:dw|
LynFran
  • LynFran
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
anonymous
  • anonymous
Sounds good, thanks a bunch :)
LynFran
  • LynFran
|dw:1435291759806:dw|
anonymous
  • anonymous
6033 _____ ? 875
anonymous
  • anonymous
^(fraction)
LynFran
  • LynFran
yes but we usually take the decimal in statistics
LynFran
  • LynFran
which is 6.894857 now this is ur chi square value
anonymous
  • anonymous
what now? is this where that "p" comes in?
LynFran
  • LynFran
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??
LynFran
  • LynFran
im seeing 0.005 on the table not 0.05
LynFran
  • LynFran
and it there twice the table have a fault
LynFran
  • LynFran
u see it? im assuming that the first 0.005 suppose to be 0.05??
anonymous
  • anonymous
Maybe it is supposed to be the 5th column?
LynFran
  • LynFran
no actually there shdnt have the same p value on a chi square table
anonymous
  • anonymous
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. :/
LynFran
  • LynFran
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
anonymous
  • anonymous
Sure thing
LynFran
  • LynFran
LynFran
  • LynFran
so |dw:1435293790254:dw|
LynFran
  • LynFran
now we compare the 2 chi square value
anonymous
  • anonymous
oh wait, so that was right? Because 6.83 > 5.99, the correct answer is either A or D?
LynFran
  • LynFran
the answer shd be D because the p value was too low
LynFran
  • LynFran
for the chi square
anonymous
  • anonymous
Both A and D say x was too low
LynFran
  • LynFran
ok u see what the difference between the two values?
anonymous
  • anonymous
One says yes, and the other says no?
anonymous
  • anonymous
referring to whether or not the model predicted the milkshake sales accurately
anonymous
  • anonymous
but i don't know how to tell that from our data/if it should be yes or no
LynFran
  • LynFran
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
LynFran
  • LynFran
ok the difference between the value is 0.84 can conclude D or A as the answer?
anonymous
  • anonymous
I understand how to get 0.84 as the difference, but not how to tell if it is Yes or No
LynFran
  • LynFran
https://www.youtube.com/watch?v=HwD7ekD5l0g
LynFran
  • LynFran
ok what we actually had to look at is if p>0.05 or p<0.05
anonymous
  • anonymous
I thought it said p=0.05 though?
LynFran
  • LynFran
yes but when we find the value we see if its greater ok lesser than 0.05
anonymous
  • anonymous
..
LynFran
  • LynFran
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
anonymous
  • anonymous
okay. what about them?
LynFran
  • LynFran
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
LynFran
  • LynFran
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
anonymous
  • anonymous
Thanks for all of your help so far @LynFran :)
LynFran
  • LynFran
ok
LynFran
  • LynFran
@jim_thompson5910
jim_thompson5910
  • jim_thompson5910
LynFran you're using the right formula \[\Large \chi^2 = \sum \frac{(O_i -E_i)^2}{E_i}\] \[\Large \chi^2 = \frac{(O_1 -E_1)^2}{E_1}+\frac{(O_2 -E_2)^2}{E_2}+\frac{(O_3 -E_3)^2}{E_3}\] \[\Large \chi^2 = \frac{(205-175)^2}{175}+\frac{(114-125)^2}{125}+\frac{(264-250)^2}{250}\] \[\Large \chi^2 = 6.894857\]
jim_thompson5910
  • jim_thompson5910
is there a typo in the table? I see 0.005 written twice along the top
jim_thompson5910
  • jim_thompson5910
I'm guessing that first 0.005 should be 0.05 ?
anonymous
  • anonymous
yes, there is
jim_thompson5910
  • jim_thompson5910
ok thought so
jim_thompson5910
  • jim_thompson5910
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
jim_thompson5910
  • jim_thompson5910
So we know test statistic = 6.89 critical value = 5.99
jim_thompson5910
  • jim_thompson5910
do you see how to finish up?
LynFran
  • LynFran
actually we did all of this is just how to compare and tell the correct answer part that a bit troublesome
jim_thompson5910
  • jim_thompson5910
Rule: if (test statistic) > (chi-square critical value), then reject the null
jim_thompson5910
  • jim_thompson5910
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
anonymous
  • anonymous
@jim_thompson5910 okay, reject the null, but we can't determine whether it would be option A or D. (Yes, or No)
anonymous
  • anonymous
from the options at the bottom of this attachment
jim_thompson5910
  • jim_thompson5910
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
anonymous
  • anonymous
Ohhhh! so it's actually B I was looking at it backwards
jim_thompson5910
  • jim_thompson5910
yeah it's B
LynFran
  • LynFran
wasnt the chic squared values 5.99? so how come that higher than 6.89??
anonymous
  • anonymous
Thank you both! I'll write your testimonials when I'm all done. (later tonight/early morning)
jim_thompson5910
  • jim_thompson5910
that 5.99 is the critical value
jim_thompson5910
  • jim_thompson5910
it's the cutoff point
anonymous
  • anonymous
I greatly appreciate all the help :)
jim_thompson5910
  • jim_thompson5910
anything higher than that cutoff point means you reject H0
LynFran
  • LynFran
o ok i see
jim_thompson5910
  • jim_thompson5910
|dw:1435292080595:dw|
jim_thompson5910
  • jim_thompson5910
|dw:1435292122002:dw|
LynFran
  • LynFran
yes ur right

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