Statistical Methods for Psychology

28 Chapter 2 Describing and Exploring Data

4.0

Score

(a) Normal

0.04

0.03

0.02

0.01

–4.0 –2.4 –0.8 0.8 2.4

25

Score

(c) Negatively skewed

0.07

0 5 10 15 20

5

Score

(e) Platykurtic

0.06

–5 –3 –1 1 3

0.06

0.05

0.04

0.03

0.02

0.01

0.05

0.04

0.03

0.02

0.01

5

Score

(b) Bimodal

0.05

0.04

0.03

0.02

0.01

–5 –3 –1 1 3

25

Score

(d) Positively skewed

0.07

0 5 10 15 20

5

Score

(f) Leptokurtic

0.09

0.08

0.07

0.06

0.05

0.04

0.03

0.02

0.01

–5 –3 –1 1 3

0.06

0.05

0.04

0.03

0.02

0.01

Figure 2.10 Shapes of frequency distributions: (a) normal, (b) bimodal, (c) negatively

skewed, (d) positively skewed, (e) platykurtic, and (f) leptokurtic

10

Reaction time

Distribution for All Trials

Frequency

500

0

20 30 40 50 60 70 80 90 100 110 120 130 140

400

300

200

100

Figure 2.11 Frequency distribution of Bradley’s reaction time data