Statistical Tests

Question 1

What is the chi squared test?

Answer 1

Uses the expected and observed values to see if there is a significant difference between them

Question 2

What is the null hypothesis?

Answer 2

Says that there is no significant difference between the values expected and observed

Question 3

What is the calculation for chi squared?

Answer 3

=£(F○ - Fe)² ÷ Fe

Fo stands for observed
Fe stands for expected

The expected value willnalways be the same for every species unless stated otherwise

Question 4

When do we reject the null hypothesis?

Answer 4

If the chi squared value is higher than the critical value at that particular degrees of freedom.

Question 5

How do you work out the degrees of freedom?

Answer 5

By subtracting 1 from the number of categories

Question 6

What do we say when we reject the null hypothesis?

Answer 6

We reject the null hypothesis because the value is higher at p=0.05. There is a 5% probability the difference I’d due to chance.

Question 7

What is standard deviation?

Answer 7

Shows us how much variation there is between the data and the mean value. It is therefore a measure of spread in the data and gives am indication of the reliability of a mean value

Question 8

How do you work out standard deviation?

Answer 8

-/£(x-x̌)² ÷ n-1

£ is the sum of
n is the number of values measured
x is each value in the data
X̌ is the mean of the data

Question 9

What can the standard deviation be used for?

Answer 9

When the mean is plotted, the standard deviation can be used to plot an error bar
50% of the data will remain on one side and the other 50% remains on the other, and the graph is symmetrical
The lower the standard deviation, the more highly clustered data will be

Question 10

How do you work out frequency density for histograms?

Answer 10

Divide the frequency by the class width
This can be used to make a normal standard deviation curve