Ecology Statistics

Question 1

What does the null hypothesis always state?

Answer 1

There is no difference between groups or correlation between variables

Question 2

P values are always between 0-1, what does the p-value mean?

Answer 2

• the probability that any observed differences or correlation in results are down to chance
• the probability that the null hypothesis is true

Question 3

What does a high p-vale of 0.98 mean?

Answer 3

That the results are most likely due to chance and the null hypothesis is true

Question 4

If you have a p-value of 0.04, and the cut off value is 0.05, what can be concluded?

Answer 4

There is enough evidence to suggest there is a correlation in the data, so we reject the null hypothesis

Question 5

When would we use a t-test?

Answer 5

When comparing the means of 2 experiments

Question 6

How do we set up for a t-test?

Answer 6

We need 3 new rows of data:
1) the mean of each data set (M1,M2)
2) the standard deviation for each set (S1,S2)
3) the number of measurements in each set (n1,n2)
Then after calculating the t-test workout the degrees of freedom
DOF=n1+n2-c

Question 7

What is the degree of freedom used for?

Answer 7

Once obtained, look in a table and find the critical value of your degree of freedom, then compare your p-value with this, if p>CV then reject null

Question 8

When should spearmans rank be used?

Answer 8

When looking for a correlation between 2 sets of continuous data

Question 9

How do we set up a spearmans rank test?

Answer 9

Add 3 new columns:
1) rank the order of data set 1
2) rank the order of data set 2
3) difference in ranks squared
Add up the squared differences (D)

Rs=1-((6xD)/n^3-n)