# Notation question

1. Jan 22, 2009

### engineer23

What is the difference between Yi (capital Y, subscript i) and yi (lowercase y, subscript i)?
Is Yi a random variable while yi is a part of a set?

2. Jan 23, 2009

### winterfors

In most cases, Y_i refers to the random variable (i.e. the probability distribution) and y_i to an observation of that variable (e.g. a numerical value).

3. Jan 23, 2009

### stewartcs

The y is the value that Y takes on.

CS