# causal

#### xmc

##### New member
which relationship can best described as causal?
(1)height and intelligence
(2)shoe size and running speed
(3)number of correct answers on a test and test score
(4)number of students in a class and number of students with brown hair

#### mmm4444bot

##### Super Moderator
Staff member
How has your class defined a casual relationship?

no

#### Denis

##### Senior Member
No? So what's your question?

#### mmm4444bot

##### Super Moderator
Staff member
Okay -- I think that I get it now. I didn't make the connection before with the typo.

We can think of causal relationships as dependencies. In other words, in a causal relationship, one thing depends upon the other, or is caused by the other.

Let's look at the first choice (a) height and intelligence.

Can we say that either one "causes" the other.

Does a person's height depend upon their intelligence (as if we needed to be smart, in order to be tall, or something like that)?

Looking at it the other way around, does a person's intelligence depend upon their height (as if we needed to be tall, in order to be smart)?

The answers to these questions is definitely NO. There is no dependency between them. A person's height does not depend upon their intelligence. A person's intelligence does not depend upon their height.

So, look at all the choices again, and try to think in terms of whether or not one thing depends upon the other.

This exercise is getting you ready for a concept in mathematics known as "function".

In a function, one quantity depends upon the other.

Here are some examples of these "causal" relationships.

(1) At the grocery store, the amount that you pay for a bunch of bananas depends upon how much the bunch weighs. Therefore, we say that this amount is a function of weight.

(2) The time it takes for you to walk to school depends upon how fast you walk. Therefore, we say that this time is a function of your speed.

(3) The number of songs that you can store on your old iPod depends upon the iPod's disk-drive size. Therefore, we say that this number of songs is a function of the storage space size.

We would not say that the weight of some bananas depends upon money; that does not make sense.

We would not say that the size of a disk drive maufactured somewhere in Taiwan depends upon the number of songs that you have at home. How could it? Taiwan doesn't know how many songs you own.

It would be just as silly to say something like, "Well, there are 25 students in this class, so that must mean that 10 students have brown hair".

Peoples' hair color is determined at conception by genetics, not by the number of students in some class that's held 16 years later.

This notion of "what is a function of what" is very important in mathematics, to be able to describe cause-and-effect in the real world.

MY EDIT: Deleted misleading sentence about properly-fitting shoes.

#### mmm4444bot

##### Super Moderator
Staff member
Denis said:
No? So what's your question?
Denis, the OP had originally typed "casual relationship" in the body of their post. I didn't recognize that as a typographical error (since edited by the OP), and, not knowing for sure what a "casual" relationship is, asked.

(BTW: In general, I ignore subject lines on these boards.)

Then, I think the OP misread my question (i.e. "Has your class" versus "How has your class"), and that's why they answered "no".

Confusion at both ends (heh, heh). I hope we're all on the same page, now.