Contingency table chi-square test | Probability and Statistics | Khan Academy

Contingency Table Chi-Square Test

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[DCSY]

You taught me an entire semesters worth of content in a few hours. bless your soul

[rolemodel]

this is still doing mighty wonders. thanks, Proff...

[whyteart]

Thanks for this. Just sorted my assessment for this week.

[kalleidoskop]

Brilliant! You explain it so well, thank you! I just might pass after all..

[Qomri]

So impressed by this Khan guy, he literally knows everything single shit no matter what you are searching for, his videos will pop up. Thank you very much though :)

[norwayte]

Could you explain more precisely the difference of
test - Goodness of fit (is distribution the assumed) and
test - (In-)dependence of two "things" (contingency table...) of
the chi square test?

Keep on going.

[lisatibbitts]

Around 4:45 It is said that 80 out of 380 did not get sick but 80 is in the sick row. Or am I not understanding the row label? Confused

[BodModGuy]

In my stats class the professor said NO DECIMALS. Bc you can't have a % of a person. Chi squared is a counting system...

[joem]

It seems like this video (and others) focus a bit too much on talking through basic arithmetic. It could be more concisely presented by showing a few examples and fast-forwarding through repetitive content (including repeating what you're writing down because we talk faster than we write). This is especially true in previous videos in this series. Sometimes you say what you're going to multiply to another number 3 times and repeat the result more than 2 times.

[sixStringsforWords]

Aren't you assuming the herbs don't work when you use 80/380 even though you have no information about it before knowing the result of the test?

Seems more logical to me to use the 30/120 ratio to calculate expected values. Could you clarify?

[marlenirigoyen]

10 years later and you still saved my grade :')

[LifeOnLine]

if the herbs do nothing would you not Expect them to have the same %'s as the plecebo, not the totals?

[divyanaik]

I don't understand how the expected proportion can be the proportion calculated from the total of the samples. Could use some more clarification on that. The contingency table is easy to understand though.

[mrjohnzon]

I have the exact same question. Good that someone else saw it aswell.

[edwardroberts]

Ok, so in this video you were comparing the actual results vs expected results from the placebo and H1 and H2 groups. However, although in this example everything is very balanced and even, how robust is the test against a strong placebo effect or herb effect (in this example). In other words, why don't you compare the data obtained against people getting sick without placebo and without herbs, what if the herbs and the placebo are all protecting people in a statistically significant way compared to naive population?

[hannahnelson]

The chi squared test assumes that the underlying distribution is bernoilli right? That's where the divide by expected comes from. Since we are adding bernoillis the variance can be assumed to be the mean, this allows us to use this mean to normalize our errors and get their appropriately normalized normal distributions.

I didn't understand the degrees of freedom part. Three normals is three normals right? Why would we use a distribution made of one less normal than the model we have?

[ebukadaniels]

Hello thank you for this video why is it called contingency table

[lorryzou]

Why do you use the total to calculate the expected value? I think using the placebo is more logical (ie. 30/120, 90/120).

[amandavargo]

makes sense. the first video was a little clearer however

[RazikhShaik]

When our Hypothesis is Herbs do nothing then why include placebo entries? Shouldn't we just compare the two herbs ?

If we are to include placebo shouldn't the hypothesis be herbs and place do nothing?

What if there was actually placebo effect meaning more people were not affected just by the sugar pill, will the same procedure help in figuring that out?