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โš–๏ธย Unit 6

ย ย โ€ขย ย โฑ๏ธ2 min read

6.1 Introducing Statistics: Why Be Normal?

Josh Argo

josh argo

โฑ๏ธ June 4, 2020

๐Ÿ“…โŒจ๏ธ

What Does it Mean to be Normal?

If you're looking back at the snowboarder study from the Unit 6 Overview, "being normal" here isn't referring to being regular footed as a snowboarder. ๐Ÿคฃ๐Ÿคฃ

In fact, the term "normal" has much larger statistical implications. When we are performing statistical inference, our calculations are very largely based on sampling distributions of a proportion, which yep, you guessed it, are normal curves.

Why is it Important?

If you refer back to Unit 1.1, we know that a lot of fancy Calculus calculations can allow us to calculate probabilities using these normal curves. When testing a statistical claim or estimating a population proportion, we need the normal curve to calculate the probability in our sampling distribution (see Unit 5). By taking our sample and standardizing it to a common density curve, we can use calculator functions or our z-score chart to make inference using the normal curve.

How do we know if it is Normal?

To check if our sampling distribution is normal, we need to verify that the expected successes and expected failures of our study is at least 10. This is known as the Large Counts Condition.

In formula form, this is npโ‰ฅ10 and n(1-p)โ‰ฅ10.

This verifies that our sampling distribution is normal and we can continue with z-scores to calculate our probabilities or intervals.

https://cdn.pixabay.com/photo/2015/01/05/13/43/ice-hockey-589313_960_720.jpg

image courtesy of: pixabay.com

Example

Let's say that we believe that hockey players have a 95% chance of breaking a bone at some point in their life. We decide to test that claim by taking a sample of 500 retired hockey players and asking them if they have ever broken a bone. To verify that we can use the normal curve in this test/interval, we would list the following:

โœ”๏ธ500(0.95)โ‰ฅ10 & 500(0.05)โ‰ฅ10

โœ”๏ธ475โ‰ฅ10 & 25โ‰ฅ10

Since both calculations come out to be more than 10, we can use our proportion from our sample to check if the 95% value given is actually true.

๐ŸŽฅWatch: AP Stats - Normal Distributions

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ap stats study guides

โœŒ๏ธย  Unit 2: Exploring Two-Variable Data

โš–๏ธย  Unit 6: Inference for Categorical Data: Proportions

๐Ÿ˜ผย  Unit 7: Inference for Qualitative Data: Means

โœณ๏ธย  Unit 8: Inference for Categorical Data: Chi-Square

๐Ÿ“ˆย  Unit 9: Inference for Quantitative Data: Slopes

๐Ÿงย  Multiple Choice Questions (MCQs)

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