FAQ: Hypothesis Testing - ANOVA


#1

This community-built FAQ covers the “ANOVA” exercise from the lesson “Hypothesis Testing”.

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This exercise can be found in the following Codecademy content:

Data Science

FAQs on the exercise ANOVA

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#2

I don’t get it:
In the explanation: “The null hypothesis, in this case, is that all three populations have the same mean … If we reject this null hypothesis (if we get a p-value less than 0.05), we can say that we are reasonably confident that a pair of datasets is significantly different.”
But in the exercise:
With store_b the means are : 58.349636084 65.6262871356 62.3611731859
and p-value is 0.000153411660078 ie we can reject the null hypothesis (see above) and the samples are different.
With store_b_new the means are: 58.349636084 148.354940186 62.3611731859
and p-value is 8.49989098083e-215 ie we cannot reject the null hypothesis (see above) and the samples are basically the same.
Surely that is the wrong way round?


#3

No, it’s correct.

The null hypothesis in this case is “There is no significant difference in sales between the stores.”

Rejecting the null hypothesis (p-value < 0.05) would mean there IS a significant difference between the at least one store.

The new sales numbers for Store B easily pass the eye test and you’d expect to reject the null hypothesis. And that’s exactly what happened in the ANOVA test (p-value = 8.49989098083e-215). You would say that there is a 99.999999…% chance that a store is significant.


#5

I found myself still confused as to how the p-value was less than 0.05 until I learned what the “e-” means. This wasn’t taught anywhere in the Data Science path prior to this exercise so I am posting it here in case it is new to anyone else.

Basically, the “e-” format in this case tells you that the p-value is 8.49989098083 times 10^-215, so it is 0 point followed by 214 zeroes and then 849…

In the project that comes after the end of this module, there is a p-value of 2.74631179866e-10. So, this should be read as the p-value equaling 0.000000000274631178966.