18. Video: Random Variables

Example to Introduce Notation

There is a lot going on in this video - here is a recap of the big ideas.

Rows and Columns

If you aren't familiar with spreadsheets, this will be covered in detail in future lessons. Spreadsheets are a common way to hold data. They are composed of rows and columns. Rows run horizontally, while columns run vertically. Each column in a spreadsheet commonly holds a specific variable, while each row is commonly called an instance or individual.

The example used in the video is shown below.

| Date | Day of Week | Time Spent On Site (X) | Buy (Y) |
|---|---|---|---|---|
| June 15 | Thursday | 5 | No |
| June 15 | Thursday | 10 | Yes |
| June 16 | Friday | 20 | Yes |

This is a row:

| Date | Day of Week | Time Spent On Site (X) | Buy (Y) |
|---|---|---|---|---|
| June 15 | Thursday | 5 | No |

This is a column:

Before Collecting Data

Before collecting data, we usually start with a question, or many questions, that we would like to answer. The purpose of data is to help us in answering these questions.

Random Variables

A random variable is a placeholder for the possible values of some process (mostly… the term 'some process' is a bit ambiguous). As was stated before, notation is useful in that it helps us take complex ideas and simplify (often to a single letter or single symbol). We see random variables represented by capital letters (X, Y, or Z are common ways to represent a random variable).

We might have the random variable X, which is a holder for the possible values of the amount of time someone spends on our site. Or the random variable Y, which is a holder for the possible values of whether or not an individual purchases a product.

X is 'a holder' of the values that could possibly occur for the amount of time spent on our website. Any number from 0 to infinity really.