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Old 06-15-2019, 01:27 PM
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ActuarybyInduction ActuarybyInduction is offline
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Default September 2019 Progress Thread

Creating a thread for the September sitting.
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Old 06-28-2019, 10:47 PM
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Default Lower bound of leverage

Is there any reason why the lower bound of a leveraged point h_ii is 1/n instead of 0?

If we look at the variance of the residual var(e_i) = sigma^2 x (1-h_ii); isn't it possible for h_ii = 0 and thus var(e_i) = sigma^2?

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Old 06-29-2019, 04:23 AM
ambroselo ambroselo is offline
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Quote:
Originally Posted by ActuarybyInduction View Post
Is there any reason why the lower bound of a leveraged point h_ii is 1/n instead of 0?

If we look at the variance of the residual var(e_i) = sigma^2 x (1-h_ii); isn't it possible for h_ii = 0 and thus var(e_i) = sigma^2?

Thanks
The proof of the lower bound is mainly matrix algebra that isn't required for the exam. To get some ideas, look at the formula of the leverage for simple linear regression, or equation (3.2.1) in the ACTEX manual. The second term, (x_i - bar(x))^2 / S_xx, is non-negative, so the leverage is at least 1/n. Equality holds if and only if x_i is exactly equal to the sample mean bar(x).
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Old 07-05-2019, 05:42 PM
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Thanks. This helped.
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Old 08-28-2019, 11:45 PM
TheActuarialNoob TheActuarialNoob is offline
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1 week till the exam window. How is everyone feeling?
Personally, I feel unsure if I'm prepared or not. There aren't enough practice problems to get a feel for the true nature of the exam.
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Old 09-15-2019, 08:27 PM
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Any reactions from the September sitting? I'm still spooked out that the SRM threads get no love...

I found that it was, more or less, what I expected. I nailed all fifteen-ish computational questions that came my way, would estimate that I also nailed 5-10 of the conceptual, and was able to narrow down the remaining 10-15 conceptual questions down to two or three options.

Wondering if anyone was surprised (pleasantly or unpleasantly) by the sitting or if, like me, it was kind of like you thought it might be.
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Old 10-11-2019, 01:34 AM
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Thanks for checking in. For me work picked up a lot before the exam and unfortunately I couldn't shift things around to get the necessary study time, so I pushed my sitting to January. Good news is that work has lighten up significantly and I plan to have sufficient time to prepare.

I'll be on this thread much more over the next few months and will definitely provide feedback on the exam.
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Old 10-17-2019, 02:29 PM
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Going for the January sitting here, doesn't seem like much is happening on the SRM threads lol... A little over halfway through the ASM manual (I've seen negative stuff about their manual for this one but I've been using it with too much success on everything else to abandon it now). Really flying through the material, thinking about using Adapt and reading through ISL once I exhaust this manual.
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Old 10-22-2019, 12:48 AM
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Actex Example 3.2.1 - Can anyone provide guidance on this one? I understand the model solution, but I'm curious as to why I can't back into y1_hat using the property that the residuals sum to 0. The model solution solves for the parameters b_0 and b_1 using LSE and gets y_1hat using x_1, which makes sense, but I thought my approach would also be adequate however I'm coming with a different value for y_1hat.
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