Name: Analysis of Variance (ANOVA)
Uploaded: 2016-09-19T22:42:37.000Z
Duration: 4 min 47 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

So you set up an experiment with three groups of people.

The second group gets some sugary fruit juice,

And you want to know if there's any difference

The null hypothesis says that the mean reaction time

because the drinks you gave each group are different.

You can see that there's a lot of variation

some people are faster and some are much slower.

But all the groups look pretty much alike;

there's not much variation between the groups.

In this case, you'd say that most of the difference

which is that the type of drink doesn't have

Now let's look at a different set of numbers.

In this case, all the scores within each group

There's not a lot of variance within each group,

but the groups are very different from one another.

There's a lot of difference between the groups.

In this case, you would reject the null hypothesis.

In this case, the type of drink makes a big difference.

So here's the idea behind analysis of variance:

Figure out how much of the total variance comes from the between-groups variance

that the means of the groups really *are* different,

and that you should reject the null hypothesis.

In the examples, it was obvious where the variance was.

more variance within groups or between groups,

The calculations show that the ratio is 4.27,

so in this case, you can reject the null hypothesis.

With these numbers, the drink you give the people

does have an effect on their reaction time.

And here's how you calculate the degrees of freedom

when you report results for analysis of variance.

not only when you have three or more groups,

it also works when you have multiple variables.

and you test another three groups in the evening,

or if the time of day makes a difference,

For example, coffee might be more effective in the morning than in the evening.

So to recap, here's the main idea of analysis of variance:

You figure hοw much of the total variance

and how much comes from within the groups.

If most of the variation is between groups,

if most of the variation is within groups,

there's probably not a significant effect.

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Analysis of Variance (ANOVA)

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