# What is Var XY equal to?

## What is Var XY equal to?

Var[X+Y] = Var[X] + Var[Y] + 2∙Cov[X,Y] . Note that the covariance of a random variable with itself is just the variance of that random variable.

What does Var y mean?

verb (used with object), var·ied, var·y·ing. to change or alter, as in form, appearance, character, or substance: to vary one’s methods. to cause to be different from something else: The orchestra varied last night’s program with one new selection.

### Can Var be negative XY?

Variance of X−Y cannot be negative.

What is the variance of Var XY?

Var[X+Y] = Var[X] + Var[Y] + 2∙Cov[X,Y] . Note that the covariance of a random variable with itself is just the variance of that random variable. While variance is usually easier to work with when doing computations, it is somewhat difficult to interpret because it is expressed in squared units.

## How do you interpret a covariance matrix?

Interpret the key results for Covariance

1. If both variables tend to increase or decrease together, the coefficient is positive.
2. If one variable tends to increase as the other decreases, the coefficient is negative.

How do you interpret variance?

To find the variance, take a data point, subtract the population mean, and square that difference. Repeat this process for all data points. Then, sum all of those squared values and divide by the number of observations. Hence, it’s the average squared difference.

### How do you read statistical notation?

Their sample counterparts, however, are usually Roman letters. For example, μ refers to a population mean; and x, to a sample mean. σ refers to the standard deviation of a population; and s, to the standard deviation of a sample.

Can a measure of variability be negative?

The answer: No, variance cannot be negative. The lowest value it can take on is zero.

## Can variance be negative stats?

Every variance that isn’t zero is a positive number. A variance cannot be negative. That’s because it’s mathematically impossible since you can’t have a negative value resulting from a square. Variance is an important metric in the investment world.

Are XY and X Y independent random variables?

Two jointly continuous random variables X and Y are said to be independent if fX,Y (x,y) = fX(x)fY (y) for all x,y. It is easy to show that X and Y are independent iff any event for X and any event for Y are independent, i.e. for any measurable sets A and B P{(X ∈ A)∩(Y ∈ B)} = P(X ∈ A)P(Y ∈ B).