Paired T-Test (Page 2 of 2) in pdf

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Correlation

When we are interested in the relationship between two continuous variables, we use correlation.

Here, we want to test whether, within plots with pawpaws, the density of pawpaw stems is related to

the density of tree seedlings. If pawpaws inhibit tree regeneration, then we expect a negative

correlation.

In SPSS, make a scatterplot of pawpaw stem density vs. tree seedling density (Graphs; Legacy Dialogs;

Scatter/Dot; Simple Scatter).

Does it look like there is a relationship between these two variables? What kind of relationship? Write

down your expectation:

_____________________________________________________________________________________

Now perform a correlation. What is the null hypothesis for the test? The alternative hypothesis?

Ho:__________________________________________________________________________________

Ha:__________________________________________________________________________________

Click Analyze; Correlate; Bivariate.

Examine the results: Pearson correlation coefficient=_____________, P=______________,

N=______________.

Do we reject the null hypothesis? Yes or No

What does the outcome of the correlation tell us about the answer to our original ecological question

about pawpaws? Write a results statement in the format: Result (Pearson correlation coefficient =___,

P=___, N=___; Figure 1). (This statement refers to your scatterplot as Figure 1).

Paired T-Test Page 2