Main content

### Course: AP®︎/College Statistics > Unit 1

Lesson 4: Statistics for two categorical variables# Conditional distributions and relationships

## Example: College grades

A small private college was curious about what levels of students were getting straight A grades. College officials collected data on the straight A status from the most recent semester for all of their undergraduate and graduate students. The data is shown in the two-way table below:

Undergraduate | Graduate | Total | |
---|---|---|---|

Straight A's | |||

Not | |||

Total |

## Want to join the conversation?

- In the answer options of the problem 4, what is the difference between the option B and C? I think both answers are correct. Are not they?(41 votes)
- Choice C is like this :

C: Straight A students ( Total is 300 students ) were more likely to be graduate ( 60 students) than undergraduate ( 240 students) !

in other words; if all students who got Straight A (graduate + undergraduate) gathered in one class, then most of them would be graduate or undergraduate?(23 votes)

- Example problems are helpful and all, but how come there aren't any written definitions for what Marginal and Conditional Distribution are?(31 votes)
- Yes, they are not very straightforward. I use statology.com to help with definitions, because math has so many. Marginal distributions compare one variable to a whole population. Ex: number of females in U.S versus the whole U.S population. Conditional distributions compare a variable to a subpopulation. Ex: Proportion of women in the U.S who are married.(21 votes)

- The wording is SO confusing to me.

You wrote in Problem 3:

"Calculate the conditional distribution of straight A status for each level of student."

How do I know if I should focus on the OF (straight A) or the FOR (each level of student)? Do I calculate row or column?

Either I am stupid in English or it is really confusing.

Please someone help me?(25 votes)- We're finding the conditional probability of x (the numerator) for
**each**of y (clue that it should go in the denominator).

If they asked "Find the conditional probability of level of study for straight A status" then these would be reversed.(6 votes)

- Why is there an association? There is only a 6% difference between undergraduates with all A's and graduates with A's. That is almost an opinion based question(7 votes)
- Yes, the difference is only 6%, but graduates are twice as likely to have straight A's than undergraduates are, which is a rather large relative difference.(4 votes)

- Hello,

I'm looking into doing AP Statistics next year, for my senior year of high school, and am wondering what prerequisites I need. Algebra 1? Algebra 2? Geometry? Precalc? Calc?

Thank you in advance!

Isabella(4 votes)- I did Alg 1 through Geometry before I did AP Stats, but you certainly don't need any sort of calculus class to do AP Stats.(5 votes)

- what does * in counts * mean(2 votes)
- Instead of percentage, it is just asking how many times it occurs(9 votes)

- I believe that Problem 2 is ambiguous, as it asks for one correct answer which is C, but both B and C appear to be correct answers. B says "There are far more students without straight A's than there are with straight A's.", which seems to be true, given a ratio of 4200 to 300.(0 votes)
- From the author:Problem 2 asks what conclusion we can draw from the highlighted distribution, and the highlighted distribution only tells us about the ratio of undergraduate to graduate students.(12 votes)

- In the solution to pb 4 an explanation is given for why answer C is false, they do the calculation 240/360= 67%, where does the 360 come from? Why isn’t it being divided by the 300 instead?(3 votes)
- This just seems like a typo tbh, but the explanation is still valid when we use 300 instead(2 votes)

- this was tough but I got it though(3 votes)
- Gold star ʕ•́ᴥ•̀ʔっ⭐(2 votes)

- The explanation of the first example states that "A conditional distribution turns each count in the table into a percentage of individuals who fit a specific value of one of the variables.", but in the exercise the values aren't always percentages; just counts! Is the article definition incorrect?(3 votes)
- From the author:That definition is correct! The first conditional distribution in this article appears in Problem 3.(1 vote)