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# CourseErrors Found in 2021 Study Materials P1.T2. Quantitative Methods

#### Nicole Seaman

##### Chief Admin Officer
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Please use this new thread to let David and I know about any errors, missing/broken links, etc. that you find in the 2021 materials that are published in the study planner under P1.T2. Quantitative Methods. This will keep our forum much more organized. We appreciate your cooperation! PLEASE NOTE: Our Practice Question sets already have links to their specific forum threads where you can post about any errors that you find. This thread is for any other materials (notes, spreadsheets, videos, etc.) where you might find errors.

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#### timpani85

##### New Member
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not sure if i am correct but here goes.

page 3 of notes QA-4-Multivariables
-Be able to manipulate the fundamental probability relationship: conditional equals joint
divided multiplied by marginal; i.e., P(B|A) = P(B ∩ A) × P(A)

believe for the equation should be P(B|A) = P(B ∩ A) / P(A) ?

Thank you.

#### RSchwarzer

##### New Member
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Hi David,

not sure if this is an mistake or I simply do not get it.

Part One T2 QA Chapter 12 Measuring Return, Volatility, and Correlation: Page 7

Within the example it states:
Continuing from the previous case of a daily volatility equal to 3.0%, we can say that the standard deviation of the continuously compounded return over five days (T = 10) is √10 × 3.0% = 9.49%.

If we compute the std dev for 5 days should it not be (T = 5) is √5 × 3.0% = 6.708%?
The following calculation are also for 10 days, so I guess it is just wrong within the text.

Thank you in advance

#### bollengc

##### New Member
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not sure if i am correct but here goes.

page 3 of notes QA-4-Multivariables
-Be able to manipulate the fundamental probability relationship: conditional equals joint
divided multiplied by marginal; i.e., P(B|A) = P(B ∩ A) × P(A)

believe for the equation should be P(B|A) = P(B ∩ A) / P(A) ?

Thank you.
on that same page, the following formula is written:
Variance of two-asset portfolio return is given by I guess it should be (1-w)^2 in front of Sigma_2^2

the same formula appears as well on page 16, with the same typo.

thanks

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#### bollengc

##### New Member
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hello,

on T2-QA-4-Multivariate-Variables-v3.4, I have noticed some small typos
page 10: first part should be Cov[X_1, X_1]

page 11: in the section X & Y are independent, only the first rule (cov(X,Y)=0) is linked to independence.
the other 2 bullet points are generic properties of covariance.

page 16:
current formula is: I would replace the 1st part with V[a*X_1 + b*X_2]
thanks

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#### bollengc

##### New Member
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hello,

on T2-QA-9-Reg-Diagnostics-v3.2, I have found the following typos:

page 4: the regression formula should include gamma_i and not Y_i, like in Garp's chapter 9: page 10: the square (crossed in red) can be removed as well, there is sometimes inconsistence in notations between the chapters (I guess it is the same in GARP), sometimes k is the nb of slop coefficient (so in chapter 8 we consider k+1) and sometimes, like here, k is the nb of coefficient (in the example, there is 1 slope coefficient and 1 intercept and k is taken equal to 2)

Page 11: still references GARP chapter 7, should be chapter 9

thanks,
Camille

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#### bollengc

##### New Member
Subscriber
hello,

I am not sure where to put that question (as it might not refer to any typo but is more a question on an example in chapter 9)

when going through Chapter 9 and having a look at the example to compute Cook's distance with the outlier page 11 (data from GARP), I do not get why we use n=15 and not n-1=14 to compute s^2 that is the estimate of the error variance from the model that uses all observation (from the sample data). I understand you are matching GARP computation that is using n=15. But would not that be 'more' correct to use n-1?
(+ the usage of k sometimes as nb of slope coefficient and sometimes as nb of coefficients in the regression model as stated in my message above)

thanks,
Camille