Statistical Methods for Psychology

Key Terms 55

Exercise 3.42.) Later in this book you will see how to use other nonlinear transformations

(e.g., square root or logarithmic transformations) to make the shape of the distribution

more symmetrical.

Postintervention weight

Weight gain relative to

preintervention weight

Weight gain from pre-

to post-intervention

70 –0.2 –0.1 0 0.1 0.2 0.3

15

12

10

8

6

4

2

0

10

Frequency 5 Frequency

12

10

8

6

4

2

0

Frequency

0

80 90 100

Posttest gainpot

–10 0 10 20 30

gain

110

Figure 2.16 Alternative measures of the effect of a cognitive-behavior intervention on weight in anorexic girls.

Key Terms

Frequency distribution (2.1)

Histogram (2.2)

Real lower limit (2.2)

Real upper limit (2.2)

Midpoints (2.2)

Outlier (2.2)

Kernel density plot (2.3)

Stem-and-leaf display (2.4)

Exploratory data analysis (EDA) (2.4)

Leading digits (2.4)

Most significant digits (2.4)

Stem (2.4)

Trailing digits (2.4)

Less significant digits (2.4)

Leaves (2.4)

Symmetric (2.5)

Bimodal (2.5)

Unimodal (2.5)

Modality (2.5)

Negatively skewed (2.5)

Positively skewed (2.5)

Skewness (2.5)

Kurtosis (2.5)

Mesokurtic (2.5)

Platykurtic (2.5)

Leptokurtic (2.5)

Sigma ( ) (2.6)

Measures of central tendency (2.7)

Measures of location (2.7)

Mode (Mo) (2.7)

Median (Mdn) (2.7)

Median location (2.7)

Mean (2.7)

Trimmed mean (2.7)

Dispersion (2.8)

Range (2.8)

Interquartile range (2.8)

First quartile, Q1 (2.8)

Third quartile, Q3 (2.8)

Second quartile, Q2 (2.8)

Winsorized sample (2.8)

Mean absolute deviation (m.a.d.) (2.8)

Sample variance ( ) (2.8)

Population variance ( ) (2.8)

Standard deviation (s) (2.8)

Coefficient of variation (CV) (2.8)

Sufficient statistic (2.8)

Expected value (2.8)

Unbiased estimator (2.8)

Efficiency (2.8)

Resistance (2.8)

Degrees of freedom (df) (2.8)

Boxplots (2.9)

Box-and-whisker plots (2.9)

Quartile location (2.9)

Inner fence (2.9)

Adjacent values (2.9)

Whiskers (2.9)

Deciles (2.11)

Percentiles (2.11)

Quantiles (2.11)

Fractiles (2.11)

Linear transformations (2.12)

Reflection (2.12)

Deviation scores (2.12)

Centering (2.12)

Standard scores (2.12)

Standardization (2.12)

Nonlinear transformation (2.12)

s^2

s^2

g