Mistake in the variance video at 5:50min

Course Q&A Math for Machine Learning Probability & Statistics for Machine Learning &...
1

At 5:50 of the variance video, it was stated that E[X2] = 5, which is incorrect.

The example gave +$4 and +$6 for each of the outcomes. If it were 4 and 6, you will have

E[X2]= (4+6)/2 = 5

But that is incorrect because Game 2 is -$4 for Tails and +$6 for Heads. Then, E[X2] should be :E[X2] = (-4 +6)/2 = 1

This will lead to the conclusion that Game 2 is RISKER than Game 1 because the dispersion from the mean for Game 2 is magnitude 5 and the dispersion from Game 1 from the mean is magnitude 1.

2

Hi @Kevin_Shey!

Actually the game should be Win 6 and Lose 4. It is a typo in the video that is already being fixed.

We are sorry for the inconvenience!

Thanks,
Lucas

3

Thank you for fixing it.

I do want to highlight that it is not just a typo problem. The lecture content actually uses the incorrect numbers (Win 6, Win 4) to draw the conclusion that both Game 1 & 2 are equally risky, which is incorrect and will be very confusing to the students.

Please highlight this to the class.

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