Chisquared

How to do the chi-squared test

What is the chi-squared test?

A chi-square test is a statistical test used to compare observed results with expected results. The purpose of this test is to determine if a difference between observed data and expected data is due to chance, or if it is due to a relationship between the variables you are studying.

Equation to analyze if differences in data due to chance or a variable being tested.

Variables

x²= chi square

E (weird e)= sum, we are gonna sum all the #

O= observed data

E= expected value

we are analyzing teh observed vs the expected values.

Example question: Flipping a coin

Heads:

E: 50

O: 53

Tails:

E: 50

O: 47

Degrees of freedom

The number of variables or N-1

example above:

N=2 (N of outcomes is 2, heads or tails)

Degrees of freedom: 2-1=1

We are on the first degree of freedom (use the first line)

chi-square(x²)= 0.36

In AP bio we use 0.05 as our confidence rate (our P value) That means our critical value for our data will be 3.841

Where does this 0.36 fall in this first degree of freedom.

Look at if it is larger or smaller than the numbers on the first degree line.

P-value > 0.05

• need to know if it is larger or smaller than 0.05. Not what it is exactly

We fail to reject the Null hypothesis beacuse its larger than 0.05.

Null hypothesis

there is no significance between the expected and observes data (value)