Lab 1G: What’s the FREQ?
Lab 1G  What's the FREQ?
Directions: Follow along with the slides, completing the questions in blue on your computer, and answering the questions in red in your journal.
Clean it up!

In Lab 1F, we saw how we could clean data to make it easier to use and analyze.
– You cleaned a small set of variables from the American Time Use (ATU) survey.
– The process of cleaning and then analyzing data is very common in Data Science.

In this lab, we'll learn how we can create frequency tables to detect relationships between categorical variables.
– For the sake of consistency, rather than using the data that you cleaned, you will use the preloaded ATU data.
– Use the
data()
function to load theatu_clean
data file to use in this lab.
How do we summarize categorical variables?

When we're dealing with categorical variables, we can't just calculate an average to describe a typical value.
– (Honestly, what's the average of categories orange, apple and banana, for instance?)

When trying to describe categorical variables with numbers, we calculate frequency tables
Frequency tables?

When it comes to categories, about all you can do is count or tally how often each category comes up in the data.

Fill in the blanks below to answer the following: How many more females than males are there in our ATU data?
tally(~ ____, data = ____)
2way Frequency Tables

Counting the categories of a single variable is nice, but often times we want to make comparisons.

For example, what if we wanted to answer the question:
– Does one
gender
seem to have a higher occurrence of physical challenges than the other? 
We could use the following plot to try and answer this question:
bargraph(~phys_challenge  gender, data = atu_clean)

The split
bargraph
helps us get an idea of the answer to the question, but we need to provide precise values. 
Use a line of code, that’s similar to how we facet plots, to obtain a
tally
of the number of people with physical challenges and their genders. Write down the resulting table.
Interpreting 2way frequency tables

Recall that there were 1153 more women than men in our data set.
– If there are more women, then we might expect women to have more physical challenges (compared to men).

Instead of using counts we use percentages.

Include:
format = "percent"
as an option to the code you used to make your 2way frequency table.– Does one
gender
seem to have a higher occurrence of physical challenges than the other? If so, which one and explain your reasoning? 
It’s often helpful to display totals in our 2way frequency tables.
– To include them, include
margins = TRUE
as an option in thetally
function.
Conditional Relative Frequencies
 There is as difference between
phys_challenge  gender
andgender  phys_challenge
!tally(~phys_challenge  gender, data = atu_clean, margin = TRUE) ## gender ## phys_challenge Male Female ## No difficulty 4140 5048 ## Has difficulty 530 775 ## Total 4670 5823 tally(~gender  phys_challenge, data = atu_clean, margin = TRUE) ## phys_challenge ## gender No difficulty Has difficulty ## Male 4140 530 ## Female 5048 775 ## Total 9188 1305
Conditional Relative Frequencies, continued

At first glance, the twoway frequency tables might look similar (especially when the
margin
option is excluded). Notice, however, that the totals are different. 
The totals are telling us that
R
calculates conditional frequencies by column! 
What does this mean?
– In the first twoway frequency table the groups being compared are
Male
andFemale
on the distribution of physical challenges.– In the second twoway frequency table the groups being compared are the people with
No difficulty
and those thatHas difficulty
on the distribution of gender. 
Add the option
format = "percent"
to the firsttally
function. How were the percents calculated? Interpret what they mean.
On your own

Describe what happens if you create a 2way frequency table with a numerical variable and a categorical variable.

How are the types of statistical investigative questions that 2way frequency tables can answer different than 1way frequency tables?

Which
gender
has a higher rate of part time employment?