PSYC 209 - 1638
Variables and Validity
27
Relationships Between Variables • Positive Relationship
– As one variable increases, so does the other variable
Ex. Professor‐student rapport and professor’s responsiveness (Wilson, Ryan, & Pugh, 2010)
• Negative Relationship – As one variable increases, the
other decreases
Ex. Self‐esteem & death anxiety (Greenberg et al., 1990)
0
5
10
15
20
25
30
1 2 3 4 5 6
0
5
10
15
20
25
30
1 2 3 4 5 6
Relationships Between Variables
• No relationship – Changes in one variable are unrelated to changes in the
other variable
Ex. Extroversion and emotional stability
0
6
1 2 3 4 5 6
Relationships Between Variables
• Curvilinear relationship – Changes in 1 variable are related to increases AND decreases in another variable
– Ex. Anxiety and performance on a task (Yerkes & Dodson, 1908)
30
Cause and Effect among Variables
Crack cocaine use during pregnancy
Birth defects, low birth weight, childhood bx
problems
r = ++
Third Variable
r = ++ r = ++
(Hurt et al., 2013)
Cause and Effect among Variables
• Nonexperimental methods – Reveal relationships between variables – Lead to predictions of behavior – Problems with causality
• Experimental methods – Direct manipulation – Control – Random assignment – Independent & dependent variables
32
Validity
• Construct – Extent to which your operational definition of the variable reflects the construct
• Internal – Extent to which you can determine a causal relationship between variables
• External – Extent to which your findings can be generalized
33
Scales of Measurement
The Numbers in Responses
Scales of Measurement
N (nominal) O (ordinal) I (interval) R (ratio)
28
Nominal
• Responses of subjects are linked to categories
• Can only tell whether something is or isn’t in a category ( = , ≠ ) – E.g., Gender:
• Claudio = male • Claudio ≠ female • Claudio ≠ other gender identity
How Many People Are/Have ‐‐
Ordinal • Categories which are ranked or have an order
• Can indicate relative standing (>, <) – In terms of who was the better chess player, Claudio > Minda
– In terms of who was the better chess player, Minda > Randy
– In terms of who was the better chess player, Claudio > Randy
Claudio = 1, Minda = 2, Randy = 3
45 > 30
30 > 0
45 > 0
Order These Pictures In Terms of The Most Extreme Hair Style…
Is the Interval Between 2 & 3 The Same As
Between 3 & 4?
2
3
4
1
Interval • Ranked categories that have equal, fixed
intervals
• Example: – Day 1 (‐20° C), Day 2 (0° C) and Day 3 (20° C) – The difference between Day 1 and Day 2 is equal to the difference between Day 2 and Day 3
– But, the “zero” is not a real zero it does not indicate complete absence
What’s in a ZERO?
Ratio
• Categories which are ordered, have an equal interval AND a true zero point
• Zero point: complete absence of the attribute being measured
• Examples: – Miles per hour ridden on a bike – Reaction times
Height, Weight, Hours, Minutes…
What Scales Are These? 38
Scales of Measurement for Four Players on a College Basketball Team
Name Average Points Scored
Points Scored (Ranking)
Position on Floor
Jordan 15 1st Shooting guard
Olajuwon 4 3rd Center
Calderón 14 2nd Point guard
Bird 8 4th Small forward
Nominal (=, ≠), Ordinal (>, <), Interval (equal, fixed but no true 0), Ratio (equal, fixed, a true 0)