Questionnaire Reliability Personality Lab October 5, 2010

Timeline for Questionnaire Assignment Oct 5 – Discuss Questionnaire Issues Oct 8 – Conduct Reliability Analyses Remove unreliable items Revise Google Docs Form i.e., subset of items from your questionnaire + items from “validity” questionnaire Send to friends & family by end of class Oct 11 – Start Final Analyses Oct 12 – Discuss Analysis Issues in Class Oct 15 – Turn in Assignment

Correlation Review Correlation Coefficient -1.00  0  +1.00 -1.00  0  +1.00 Coefficient indicates “strength of relationship” between two variables -.75 equally strong as +.75 Knowing score on one variable, what can be predicted of the other variable?

Correlation – Neuroticism and Extraversion

Correlation – Optimism & Self-Esteem

Correlation

Types of Reliability Test – Retest Internal Consistency How did your scores compare across two occasions? Internal Consistency Do all questionnaire items measure the same thing?

Satisfaction with Life 1 - Strongly disagree 4 – Neutral 7-Strongly Agree   _____1. In most ways my life is close to my ideal. _____2. The conditions of my life are excellent. _____3. I am satisfied with my life. _____4. So far I have gotten the important things I want in life. _____5. If I could live my life over, I would change almost nothing. _____6. I love SPAM.

Types of Reliability, cont. Internal Consistency Item-total correlations Satisfaction with Life Questions # 1 #2 #3 #4 #5 #6 Dana 7 1 Donna 5 6 Dan 4 3 Don 2

Types of Reliability, cont. Internal Consistency Item-total correlations Satisfaction with Life Questions with SPAM # 1 #2 #3 #4 #5 #6 Total Item Dana 7 1 35 Donna 5 6 27 Dan 4 3 19 Don 2 11

Types of Reliability, cont. Internal Consistency Item-total correlations Satisfaction with Life Questions -- Replace SPAM Item # 1 #2 #3 #4 #5 #6 Total Item Dana 7 6 35 Donna 5 27 Dan 4 3 19 Don 2 11

Internal Consistency Split-Half Reliability Spearman-Brown Formula R=2r/1 + r Split-Half Reliability Using Spearman-Brown Formula # 1 #2 #3 #4 #5 #6 1st Half 2nd Half Dana 3 5 7 6 15 17 Donna 4 11 14 Dan 2 10 8 Don 1

Internal Consistency Split-Half Reliability Spearman-Brown Formula R=2r/1 + r Split-Half Reliability Using Spearman-Brown Formula #1 #2 #3 #4 #5 #6 1st Half 2nd Half Dana 3 5 7 6 15 17 Donna 4 11 14 Dan 2 10 8 Don 1 Correlation Between 1st Half and 2nd Half r=.60

Internal Consistency Split-Half Reliability Spearman-Brown Formula R=2r/1 + r Split-Half Reliability Using Spearman-Brown Formula # 1 #2 #3 #4 #5 #6 1st Half 2nd Half Dana 3 5 7 6 15 17 Donna 4 11 14 Dan 2 10 8 Don 1 Correlation Between 1st Half and 2nd Half r=.60 R=2(.60) / 1 + .60 = 1.2/1.6 = .75

Internal Consistency Cronbach’s Alpha Average of All Split-Half Reliabilities Split-Half Reliability Using Spearman-Brown Formula # 1 #2 #3 #4 #5 #6 1st Half 2nd Half Dana 3 5 7 6 14 18 Donna 4 11 Dan 2 9 Don 1 Correlation Between 1st Half and 2nd Half r=.65 R=2(.65) / 1 + .65 = 1.3/1.65 = .79