Perceptual and Motor Skills, 2011, 113, 2, 631-646. Perceptual and Motor Skills 2011

Partial eta squared (η²; effect size) ranges from 0 to 1 and represents 
the proportion of variance in the dependent variable explained by the in-
dependent (group) variable as small (η² = .01), medium (η² = .09), and large 
(η² = .25) effects (Tabachnick & Fidell, 2007). The statistical analyses were 
carried out using SPSS Version 14 (SPSS, Inc., 2003).
Results
In the present study, 69.8% of the adolescents reported they were 
physically active 2–3 days per week (26.3% of those were physically active 
almost every day), while 30.2% reported that they were physically active 
1 day or less per week (4% of those were not physically active at all). The 
mean score for the whole sample on stress was 129.8, and the mean score 
on happiness was 7.7. Distribution of sex and age differences on the out-
come of physical activity, stress, and happiness is shown in Table 1. 
The results from correlations between age, physical activity, stress, 
and happiness are presented separately for boys and girls in Table 2. As 
shown, a weak positive, but statistically significant, correlation was found 
between physical activity and happiness, and a statistically significant 
negative correlation between stress and happiness for girls, whereas for 
boys, a statistically significant positive correlation was found between 
happiness and physical activity, and a negative statistically significant cor-
relation was found between stress and physical activity. 

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I. E
. O
. M
O
LJO
R
D
, e
T a
l.
63
8
TABLE 1
Means, Standard Deviations, and Percentage of Sex and Age Distribution of Participants in Group 1: 13–14-yr.-old,
Group 2: 15–16-yr.-old, and Group 3: 17–18- yr.-old (N = 1,508) on Physical Activity, Stress, and Happiness
Age, Physical Activity, Stress, 
and Happiness
Girls
Boys
Total
n
%
M
SD
n
%
M
SD
n
%
M
SD
Group 1: 13–14 yr.
343
44.6
349
47.5
692
46.0
Physical activity
339
3.8
1.0
342
3.9
1.1
3.9
1.0
Stress
313
137.5
51.0
306
120.6
45.4
129.0
49.1
Happiness
288
7.8
2.2
281
7.9
1.9
7.8
2.1
Group 2: 15–16 yr.
273
35.5
276
37.6
549
36.5
Physical activity
273
3.7
1.0
273
3.9
1.0
3.8
1.0
Stress
257
147.3
48.6
243
119.4
40.3
133.7
46.8
Happiness
244
7.2
2.5
224
8.0
2.0
7.6
2.3
Group 3: 17–18 yr.
153
19.9
110
15.0
263
17.5
Physical activity
152
3.7
1.0
108
3.7
1.0
3.7
1.0
Stress
142
130.4
41.9
101
113.9
41.5
123.5
43.0
Happiness
132
7.5
2.1
94
7.7
1.8
7.5
2.01
Total group
769
100.0
735
100.0
1,504
100.0
Physical activity
764
3.8
1.0
723
3.9
1.0
1,487
3.8
1.0
Stress
712
139.6
49.0
650
119.1
42.9
1,362
129.8
47.3
Happiness
664
7.5
2.3
599
7.9
1.9
1,263
7.7
2.1

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STRESS AND HAPPINESS AMONG ADOLESCENTS 
639
A one-way between-groups analysis of variance (ANOVA) was con-
ducted to investigate the association among different frequencies of phys-
ical activity when divided into three groups (Low, Moderate, High) and 
the outcome of stress and happiness scores. There was a statistically sig-
nificant difference in mean stress scores for the three groups (Table 3). The