Lab 2H  Eyeballing Normal
Lab 2H  Eyeballing Normal
Directions: Follow along with the slides, completing the questions in blue on your computer, and answering the questions in red in your journal.
What's normal?

The normal distribution is a curve we often see in real data.
– We see it in people's blood pressures and in measurement errors.

When data appears to be normally distributed, we can use the normal model to:
– Simulate normally distributed data.
– Easily compute probabilities.

In this lab, we'll look at some previous data sets to see if we can find data that are roughly normally distributed.
The normal distribution

The normal distribution is symmetric about the mean:
– The
mean
is found in the very center of the distribution.– And the curve looks the same to the left of the mean as it does on the right.

Use the following to draw a normal distribution:
plotDist('norm', mean = 0, sd = 1)
The mean and sd of it

To draw a normal curve, we need to know exactly 2 things:
– The
mean
andsd
. 
The
sd
, or standard deviation, is a measure of spread that's similar to theMAD
. 
Which part of the normal curve changes when the value of the
mean
changes? 
Which part of the normal curve changes when the value of the
sd
changes? 
Hint: Try changing the
mean
andsd
values in theplotDist
function.
Finding normal distributions

Load the
cdc
data and use thehistogram
function to answer the following: 
Think about the
height
andweight
variables. Based on what you know about these variables, which of the variables do you think have distributions that will look like the normal distribution?– Make histograms of these variables. Which ones look like the normal distribution?
– Hint: To help answer this question, try including the option
fit = "normal"
in the histogram function. You might also try faceting bygender
.
Using normal models

Data scientists like using normal models because it often resembles real data.
– But not EVERYTHING is normally distributed.

As a data scientist in training, you must decide when a normal model seems appropriate.
– No model is ever perfect 100% of the time.
– If you choose a model, you should be able to justify why you chose it.
On your own

For each of the following, determine which, if any, appear to be normally distributed. Explain your reasoning:
– The difference in
percentages
between male and female survivors in a slasher film for 500 random shuffles.– The difference in
median
fares between survivors and nonsurvivors on the Titanic for 500 random shuffles.– The difference in
mean
fares between survivors and nonsurvivors on the Titanic for 500 random shuffles. 
Hint: Refer to Lab 2E and 2F.