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PSYC 218 901 2022 Winter – Lab Assignment 2

Correlation

INSTRUCTIONS: This assignment focuses on correlation. You should review Chapter 3 of "A Student Guide to SPSS" before trying to complete this assignment. Use the SPSS file “Assignment 2 Data.sav' to complete the assignment. The data contained in the SPSS file are from the online survey your class completed. The exact wording of each question and the meaning of the values of coded variables can be found in the Variable View window. (Review the Variable View section of Chapter 1 of "A Student Guide to SPSS", if necessary).

Marking of lab assignments will be very strict. If you did not complete the Qualtrics survey on time, you will lose 1/4 of the total assignment grade (5.5 points). To avoid receiving other deductions, type your answers in the spaces provided. You may insert additional spaces after any question as needed. In addition, use proper symbols and notation (e.g., , s², z, r) in all your answers, and properly round all your answers to 2 decimal places. You will lose marks for each and every failure to follow these directions.

This lab assignment is due at the on Feb 16. Submit your assignment via Canvas. Do not email your assignment. You will lose 1/8 of the total assignment grade (2.75 points) for each day it is late. An assignment will be considered one day late as soon as the deadline passes.

1. Answer the following. [4 points]

a. Outliers (or extreme scores) are often defined as scores that are more than 3 standard deviation units away from the mean. Outliers are sometimes the result of data entry errors or participants' misunderstanding of survey items. Transform all the ‘hrsstudy’ scores to z scores. Outlier is defined as being greater than 3 standard deviations from the mean. Identify and report the CogLabID(s) and z score(s) of any outlier(s) in the data set for the variable ‘hrsstudy’. (The sort cases function in SPSS may come in handy here. Note: Missing scores are not outliers.) (1 point) 

b. Use the select cases function to select only those participants with fewer than 45 hours per week of studying. Next, create a scatter plot of the variables 'meangrade' and 'hrsstudy'. Plot the 'meangrade' variable on the Y Axis. Copy and paste the scatter plot from your SPSS output into this assignment, in the space below. (1 point)

c. Does the relationship shown in the scatter plot in question 1b appear linear? (0.5 point) Is it appropriate to calculate Pearson's r for the variables shown in the scatter plot? (0.5 point)

d. Be sure to keep on the filter that you added in question 1b (i.e., continue to select only participants with ‘hrsstudy’ less than 45) when completing the rest of the assignment. Why is it important that you do this? (1 point)

2. Calculate and report the correlation coefficients for the given pairs of variables in questions a to f. In each part, be sure to use the proper notation to identify the type of correlation coefficient. Then answer the questions in parts g to l. [9 points]

a. 'meangrade' and 'motivation' (0.5 pt) d.   ‘firstyear’ and 'extracurric' (0.5 pt)

b. 'happy' and ‘exercise’ (0.5 pt) e.   ‘thedress’ and ‘yannylaurel’ (0.5 pt) 

c. 'hotdog' and 'friends' (0.5 pt) f.   'happy' and 'belong' (0.5 pt) 

g. Interpret the correlation you reported in question 2a. (0.5 point) What conclusions can you draw? (0.5 point) 

h. Interpret the correlation you reported in question 2b. (0.5 point) What conclusions can you draw? (0.5 point) 

i. Interpret the correlation you reported in question 2c. (0.5 point) What conclusions can you draw? (0.5 point) 

j. Interpret the correlation you reported in question 2d. (0.5 point) What conclusions can you draw? (0.5 point) 

k. Interpret the correlation you reported in question 2e. (0.5 point) What conclusions can you draw? (0.5 point) 

l. Interpret the correlation you reported in question 2f. (0.5 point) What conclusions can you draw? (0.5 point) 

3. Answer the following. [4.5 points]

a. Calculate and report the correlation between 'meangrade' and 'hrsstudy'. (0.5 point) 

b. Calculate and report the correlation between 'hrsstudy' and 'motivation'. (0.5 point) 

c. Calculate and report the partial correlation between 'meangrade' and 'hrsstudy', after controlling for 'motivation'. (1.5 points) 

d. Based on the results of questions 3a, 3b, and 3c what can you conclude about the influence of motivation on the correlation between students' mean grades ('meangrade') and the number of hours per week on average they spent studying ('hrsstudy')? (2 points) 

4. Use the select cases function to select only those subjects who had a mean grade greater than 80 but also less than 90 (in other words, ‘meangrade > 80 & meangrade < 90’). Continue to remove any outlier(s) we identified in Question 1a. Answer the following. [4.5 points]

a. Calculate and report the correlation between 'meangrade' and 'hrsstudy'. (0.5 point) 

b. What percentage of the variability in 'meangrade' was accounted for by 'hrsstudy' before you selected only subjects who had a mean grade greater than 80 but also less than 90? (1 point) 

c. What percentage of the variability in 'meangrade' is accounted for by 'hrsstudy' after you selected only subjects who had a mean grade greater than 80 but also less than 90? (1 point) 

d. What phenomenon is illustrated by the difference between your answers to questions 4b and 4c? Alternatively, why are the values of the correlation coefficients so different in the two cases? (2 points)

For TA use:

Total  =       /22 points

Late Deductions (2.75 points for each day late) =

Survey Deductions (5.5 points for failure to complete on time) =

Final Assignment Grade =      /22