CORRELATION BONUS WORKCompletion = up to 20 points toward Exams

PROCESS

Choose a partner or two (no groups larger than 3)

Take out a sheet of paper and list first/last names for all group members

Questions will be posed and you as a group will develop your answers

Vocal and physical responses are required...i.e. no participation, no credit!

It’s okay to be wrong!!!! We are all here to learn and review!

CORRELATION STUDY? HOW DO YOU KNOW?

1. What words do you see in the text of a journal article or data set description that allows you to recognize the study as a correlational study?

CORRELATION EXAMPLE

We will be looking at a correlation example where we are exploring the relationships between variables.

Look at Excel

HYPOTHESIS TESTING

Step 1: State the Hypotheses2. State the null hypothesis to test the correlation

between gender and time writing is taught each week.

Ho: There is no relationship between gender and time writing is taught each week.

HYPOTHESIS TESTING

3. State the alternative hypothesis to test the correlation between gender and time writing is taught each week.

Ha: There is a relationship between gender and time writing is taught each week.

HYPOTHESIS TESTING

Step 2: Choose and have Excel compute the appropriate test statistic.

4. When we are conducting a correlation, what is our test statistic?

Correlation coefficient

HYPOTHESIS TESTING

Step 3: Determine the critical value needed to reject the Null

5. When we are conducting a correlation, what do we need to know in order to locate the critical value from the chart?

One or Two Tailed; Threshold Value (.05); and Degrees of Freedom

HYPOTHESIS TESTING

6. How do we know if our study is one-tailed or two tailed? Is our current study one or two tailed? What is our degrees of freedom

• We look at the hypotheses for directional terms. One = Directional ( greater/less than 0; Two = No Directional Terms

• Our study is two tailed because there are no directional terms in our hypotheses.

• df = 321

HYPOTHESIS TESTING

7. Looking at the Critical Value Chart B4, what is the critical value for our study?

rcritical = 0.1946

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Step 4: Compare the obtained value and the critical value and make a decision

8. What do we need to do to the obtained value before we compare the values?

Find the absolute value of the obtained value

HYPOTHESIS TESTING

9. What is the robtained?

• robtained = - 0.0541

• robtained = [- 0.0541]

• robtained = 0.0541

HYPOTHESIS TESTING

10. Compare the obtained and critical value? Which is greater? What is your decision with regards to the null hypothesis? Why?

• ro = 0.0541 < rc = 0.1946

• Fail to reject the null hypothesis• B/c the critical value is greater than

the obtained value

HYPOTHESIS TESTINGStep 5: State the conclusion

11. Based on our decision to fail to reject the null, is the relationship significant? Is p greater/less than the threshold value (.05). How do you know? What direction is the relationship between gender and time? How do you know?

• no• p > .05, because there is not a significant

relationship• Inverse, because the ro is negative.

HYPOTHESIS TESTING

12. Compute r2 =and explain how much of the variance (change in y) is explained.

r2 = .003 Less than 1% of the variance is explained (time explained by gender)

HYPOTHESIS TESTING

13. Write up your interpretation statement r(df) = obtained, p ? .05, r2 = ?

r(321) = - 0.054, p < .05, r2 = 0.003

HYPOTHESIS TESTING

14. State your conclusion like you will for the final project. State something about the decision, the direction, and the significance

We fail to reject the null hypothesis because the p value is greater than the threshold alpha. While the relationship between gender and time teaching writing each week is inverse, the relationship is not significant.

HYPOTHESIS TESTINGStep 6: If significant, then often the prediction line is

useful to state...

15. What is the prediction line (in symbols)?

• ŷ = a + bx or ŷ = bx + a

HYPOTHESIS TESTING

16. What is the prediction line for our study?

• ŷ = - 3.784x + 36.498OR• ŷ = 36.498 – 3.784x

QUESTIONS????

Fold your work in half Write the last names of the group members

on the outside. Turn in as you leave. Final Project due May 1st, 2pm.