1. Exploring the homeostatic theory of SWB in a group of adolescents
Carrie Hayward & Mark Stokes
Deakin University 2007

2. Background to research
Theory of SWB Homeostasis
SWB held within a narrow positive range 70-80% Scale Maximum
Cummins has found SWB to be held at around 75% SM in normal adults populations internationally
The system is under the control of cognitive buffers.
This study is part of a larger research project that commenced in early 2004 when SWB homeostasis was becoming a widely accepted theory in SWB literature.
Homeostatic theory suggests that SWB is actively controlled and maintained within a positive range. It began with Heading and Wearing (1992) who proposed that this homeostatic system maintains SWB at an individual and predetermined ‘set-point’. This idea was later reinforced by Cummins, who demonstrated that under normal conditions, the average measure of SWB in sample populations from Western societies is approximately 75% scale maximum, or within a 70-80% SM range, and with 40-80% defining the normative range for individuals (Cummins & Nistico, 2002).
In the Cummin’s model of SWB homeostasis, it’s suggested that positive cognitive biases work to maintain SWB in the 70-80% band.

3. Normal Distribution of SWB

4. Cognitive Buffers Personality
Work to maintain SWB in the positive 70-80% range
Past research has explored the role of personality and control constructs
Personality
Cummins, Gullone & Lau (2002) argue that personality mediates the relationship between external experiences and SWB.
Extroversion associated with positive affect,
Neuroticism associated with negative affect
However, correlations vary significantly between studies, and the role of personality factors in the maintenance of SWB is questionable.
It has been proposed that SWB is primarily under the control of a set of cognitive buffers, including personality and control factors.
In 2002, Cummins and colleagues argued that personality mediates the relationship between external experiences and SWB. Most researchers in the field have found that extroversion is closely aligned with positive affect, whereas neuroticism is associated with negative affect.
However, correlations are extremely discrepant within the literature, and the direction of the relationships is often not established. Therefore, the role of personality factors in the maintenance of SWB has been questioned.

5. Cognitive Buffers Mastery
The perceived ability to bring about desired outcomes or responses
A global construct
Refers to control over internal self as well as actual control over environmental conditions.
Viewed to be a critical mediator between life stressors and health outcomes (Pearlin & Schooler, 1978).
In terms of control constructs, the role of “mastery” was examined. Mastery concerns not only behaviour or physical outcomes or realities, but also considers the importance of mental state and emotional experience.
That is, in comparison to other measures of control, such as locus of control, primary and secondary control etc., mastery is a global evaluation, an overarching sense of the degree to which one experiences control over what goes on in his or her life (Pearlin & Skaff 1996).
Mastery does not distinguish between whether control is sourced within in the individual or the external world, but allows both to be contained within one's overall perception of control.

6. Background research
The homeostatic system can be defeated by extreme negative experiential input
Commonly observed in individuals with traumatic brain injury (TBI).
Q. Why do some individuals experience lower SWB following TBI?
However, despite the presence of psychological mechanisms to maintain SWB, the homeostatic system can be defeated by extreme negative life events or experiential input. This is commonly observed in individuals with traumatic brain injury (TBI).
Therefore, we wanted to investigate why some individuals experience lower SWB following TBI?

7. Research Project
Research into the homeostatic theory of SWB in a TBI population was conducted, to compare with normative data.
However, existing research into the SWB of adolescents was limited and normative data was not available.
The aim of this study was therefore to obtain normative SWB data for adolescents.
At the time of project commencement an area that had received little, if any at all, research attention was neural localisation of the homeostatic system. That is, does a neurological substrate for SWB exit?
We therefore decided to explore this idea in individuals with TBI who had been injured to various locations of the brain. The sample consisted of adolescents and adults from two major hospitals in Melbourne. However, at the time, there was little normative data demonstrating the existence of the set-point theory or homeostatic regulation of SWB in an adolescent population, to compare with the TBI sample. Therefore, the study presented here aimed to obtain normative SWB data for adolescents.

8. Methodology Participants
603 students (years 7 to 10) from two Melbourne schools.
Age range from yrs (M = 14.3)
480 Males & 123 Females
Procedure
All senior level students were invited to participate.
Students who provided informed individual and parental consent were included in the sample.
Paper and pencil questionnaire was completed on allocated morning during home room.

9. Measures
PWI-SC – Personal Wellbeing Index – School Children 2nd Edition (Aust. Centre on QOL, Deakin University)
How happy are you with your….
Standard of living
Health
What you achieve in life
Personal relationships
Community connectedness (“doing things away from home”)
Safety
Future security
* Participants rated each item on a 11-point Likert response scale ranging from (0) very sad to (10) very happy
SWB was measured using the Personal Wellbeing Index–School Children: 2nd Edition (PWI-SC; Cummins and Lau, 2004). The PWI-SC is a simplified item wording of the adult version (Personal Wellbeing Index-Adult; PWI-A). The PWI index scales have been developed to measure subjective wellbeing. Both scales contain seven items of satisfaction, each one corresponding to a quality of life domain: standard of living, health, life achievement, personal relationships, personal safety, community-connectedness, and future security. Participants rated each item on an 11-point Likert Response scale ranging from (0) very sad to (10) very happy, with (5) representing not happy or sad.
Basic and cumulative psychometric characteristics of the PWI scales have been published (e.g., Cummins et al., 2003), demonstrating the valid, reliable and sensitive nature of the instrument. For example, Cronbach alpha lies between 0.7 and 0.8 in Australia and overseas, and twelve surveys of the Australian population have produced a maximum variation of 3.1 percentage points in subjective wellbeing (e.g. Cummins et al., 2003). Moreover, high correlations with other quality of life measures have been reported such as .78 with the ‘Satisfaction with Life’ scale (Diener et al., 1985). Detailed data concerning scale composition, reliability, validity, and sensitivity can be found in reports of the Australian Unity Wellbeing Index (

10. e.g., "I can do just about anything I really set
Measures
2. Mastery Scale (Pearlin & Schooler, 1978)
Seven-item scale
Assesses the degree to which individuals perceive personal mastery over life outcomes
e.g., "I can do just about anything I really set
my mind to do".
* Responses were given on a 11-point Likert response scale ranging from: (0) strongly disagree to (10) strongly agree.
Mastery was measured using the Mastery Scale (Pearlin & Schooler, 1978). This seven-item scale assesses the degree to which individuals perceive personal mastery over life outcomes (e.g., "I can do just about anything I really set my mind to"). Responses were given on a 11-point Likert Response scale ranging from (0) strongly disagree to (10) strongly agree. Previous research has shown that the instrument possesses satisfactory psychometric properties (Pearlin et al., 1981; Pearlin & Schooler, 1978; Turner & Noh, 1988). This includes a Cronbach alpha of .77.

11. Measures 3. The Big-Five Abridged Scale (BFAS; Langford, 2003)
Five-item scale of the Big Five framework of personality. Each item measuring:
Openness: uncreative (0) vs. creative (10)
Agreeableness: headstrong (0) vs. gentle (10)
Conscientiousness: lazy (0) vs. hardworking (10)
Extraversion: shy (0) vs. outgoing (10)
Neuroticism: nervous (0) vs. at ease (10)
The BFAS has been found to have adequate levels in terms of: (a) convergence with widely used Big-Five measures in self, observer and peer reports, (b) test-retest reliability (mean r = .68), (c) patterns of predicted external correlates, and (d) convergence between self and observer ratings. Gosling, Rentfrow and Swann (2003) reported that the BFAS, is a reasonable proxy for the longer measure. It has therefore been concluded that use of BFAS is adequate where personality is not the primary topic of interest (Gosling et al., 2003; Langford, 2003; Paunonen & Jackson, 1985). Many researchers argue that very brief measures reduce item redundancy, reducing participant boredom, and frustration of answering the same item again and again, which is a benefit that can almost restore any psychometric costs of short measures.

12. Measures Participants were also asked:
Have you ever experienced a knock to the head that resulted in a loss of conscious?
If yes:
- Were you hospitalized?
- How long were you hospitalised for?
(no. of days/mths.)
547 participants answered ‘no’ to both questions = the normative group.
140 participants reported experiencing a knock to the head with no admission = the ambiguous group.
56 participants experienced a knock to the head and were admitted to hospital = the head injured group.
Length of stay ranged from ½ day to 30 days.
To identify those individuals who had suffered a previous injury to the head (i.e. in order to separate them from those who hadn’t and obtain a normative sample), participants were also asked the above questions. Participants who reported experiencing a previous knock to the head (N=140) with no consequential hospital admission were categorised as ‘ambiguous’ and were excluded from further analyses as it was felt that this information alone was insufficient to conclude that a head injury had or had not taken place.

13. Aims and Hypotheses of Study 1
Determine the population mean of SWB in a group of normal adolescents.
Investigate the affect of personality and mastery on SWB in adolescents
Preliminary investigation into the association between previous head injury and SWB.

14. Hypotheses of Study 1 Hypotheses
Adolescent data would replicate adult data, with SWB population mean falling within 70-80% SM range.
Personality and Mastery would be associated with SWB.
Personality and Mastery would mediate the association between previous head injury and SWB.
Hypotheses are based on the findings from previous research examining the SWB of adult populations; demonstrated normative population means (e.g., Cummins 1995; Cummins et al., 2003); homeostatic maintenance of SWB (e.g., Cummins, Gullone & Lau, 2002; Headey & Wearing, 1972); and significant relationships between SWB and personality (e.g., Diener & Lucas, 1999) and SWB and control (e.g., Cummins & Nistico, 2004)

15. Results – Hypothesis 1 Adolescent Population Means
Hypothesis 1: Mean population responses were calculated. Firstly, the results are displayed here for SWB and Mastery. It was observed that there was a difference in SWB between the two groups: normative and HI. However, both groups are falling within the 70-80% band.
Mastery was also measured on a scale distribution, and although lower than SWB, there is some indication of a relationship between the two constructs.

16. Results – Hypothesis 1 Adolescent Population Means
Population means were gathered for the five personality constructs, and it was observed that there may be a significant difference between the HI group and Non-HI group on extraversion.

17. Results – Hypothesis 1
T-Tests for Non-HI and HI mean SWB and Mastery responses
Non-HI HI t
Sig.
SWB M
77.8
75.3
1.316
.189 SD
12.9
15.9
Mastery
71.3
67.8
1.516
.130
16.3
18.5
To determine whether there were any significant differences between means for the normative compared to the HI group, t-tests were conducted. There was no significant difference between groups for SWB or Mastery.

18. Results – Hypothesis 1
T-Tests for Non-HI and HI mean Personality responses
No HI HI t
Sig.
Openness M
71.3
71.4
-.064
.949 SD
18.6
18.9
Conscientiousness
64.3
63.6
.263
.793
20.5
22.6
Agreeableness
54.9
53.2
.580
.562
Extraversion
64.8
73.4
-2.887
.004*
21.2
19.2
Neuroticism
65.3
64.6
.231
.817
20.7
23.0
There was a significant difference between the normative and HI groups on mean extraversion scores – with the HI group overall scoring higher on the extraversion scale. Does the personality disposition represented by the extraversion scale, including a predilection for stimulus seeking, high activity, sociability etc. explain this finding?
*p = 0.01

19. Results – Hypothesis 2 B  t Mastery .403 .521 15.786*** Head Injury
Standard regression analysis testing the role of Mastery, Head Injury and Personality B  t
Mastery
.403
.521
15.786***
Head Injury
-1.340
-.044
-1.014
Neuroticism
.067
.205
3.047**
Extraversion
.050
.093
2.481*
Conc.
.004
.078
.206
Openness
.053
.075
2.568*
Agreeableness
.142
.001
6.559***
A standard regression test was performed to test for the role of mastery, head injury, and personality on SWB. Some significant results emerged:
Mastery accounted for 53% of the variance in SWB.
Four of the five personality constructs accounted for a significant amount of variance in SWB.
Head Injury and agreeableness were not significant predictors.
*p<.05; **p<.01; ***p<.001

20. Results – Hypothesis 2 B  t sr² 1. Mastery .508 .639 20.342*** .408
Sequential regression analysis testing the role of Mastery and sig. Personality constructs B  t
sr²
1. Mastery
.508
.639
20.342***
.408
2. Mastery
Neuroticism
.404
.143
.507
.226
15.900***
6.619***
.209
.036
Extraversion
.050
.080
2.447*
.005
Openness
.067
.095
3.060**
.008
Conc.
.079
2.537* R²
Adj R²
 R² R
.506
.502
.098**
.711
The significant predictors were then entered into a sequential regression, with mastery entered in the first step. The four personality constructs continued to contribute a significant amount of variance even after the variance explained by Mastery was accounted for. Overall, the model explained 50% of the variance in SWB.
*p<.05, **p<.01 ***p<.001

21. Results – Hypothesis 3
Do Personality and Mastery mediate the effect of Head Injury on SWB?
Head Injury did not have a significant direct effect on SWB
However, mediation tests were carried out to determine if Head Injury had a significant indirect effect on SWB through the Personality and Mastery.
Mediation Model 1
Mediation Model 2
SWB HI
Personality
SWB HI
Mastery c c
Homeostatic theory of SWB suggests that cognitive buffers work to maintain SWB at its pre-determined set point when an individual is faced with adversive conditions. It was therefore hypothesised that Mastery and Personality would mediate the effect of Head Injury on SWB. Even though it was observed in the previous analysis that Head Injury did not have a significant direct effect on SWB, mediation tests were carried out to determine if HI had a significant indirect effect on SWB through personality and/or mastery
b (Sb)
a (Sa)
b (Sb)
a (Sa)

22. Results – Hypothesis 3 Mediation Model 1: Personality as mediator
One personality factor was extracted through the principal components method.
Personality factor explained 35.6% of variance:
²(10, N=603)= , p<.001
Sobel’s Test = To test whether a mediator carries the influence of an IV to a DV.
Prior to investigating the mediating role of personality, one personality factor was extracted from the five personality constructs. The data were analysed by means of a principal components analysis. The extracted Personality factor explained 35.6% of variance.
Mediation analyses were conducted through Sobel tests (Sobel, 1982). The Sobel test provides an approximate significance test for the indirect effect of an independent variable on the dependent variable via the mediator. The path from the independent variable to the mediator is denoted as ‘a’ and its standard error is ‘Sa’; the path from the mediator to the dependent variable is denoted as ‘b’ and its standard error is ‘Sb’.
The exact formula, given multivariate normality for the standard error of the indirect effect or ‘ab’ is shown in equation 1.
Eqn. (1)
* Sobel Test formula was drawn from MacKinnon & Dwyer (1994).

23. Results – Hypothesis 3 Sobel’s Z = 1.206 (p=.228)
Mediation Model 1: Personality as mediator
Sobel’s Z was obtained to assess whether the indirect effect of Head Injury through Personality was significant.
Path B SE
HI SWB (c)
-3.560
(-2.433)
1.599
(1.849)
HI Personality (a)
.138
.114
Personality SWB (b)
8.098
(8.160)
.570
(.569)
SWB HI
Personality c
b (Sb)
a (Sa)
Sobel’s Z was obtained to assess whether the indirect effect of Head Injury through Personality is significant. Path ‘a’ and ‘b’ (the unstandardised B-weights and their respective SE’s) were entered into an interactive calculation tool. Sobel Z was not significant (Sobel Z = 1.206, p=.228) indicating that the indirect effect of Head Injury on SWB via Personality was not significantly different from zero.
( ‘x’ ) = simple regression B weight
Sobel’s Z = (p=.228)

24. Results – Hypothesis 3 Sobel’s Z = -1.512 (p=0.130)
Mediation Model 2: Mastery as mediator
Sobel’s Z was obtained to asses whether the indirect effect of Head Injury through Mastery was significant.
Path B SE
HI SWB (c)
-.646
(.255)
1.429
(.76)
HI Mastery (a)
-3.519
2.321
Mastery SWB (b)
.508
(.508)
.025
(.025)
SWB HI
Mastery c
Sobel’s Z was obtained to assess whether the indirect effect of Head Injury through Mastery was significant. Path a and b (the unstandardised B-weights and their respective SE’s) were entered into an interactive calculation tool. Sobel Z was not significant (Sobel Z = , p=.130) indicating that the indirect effect of Head Injury on SWB via Mastery was not significantly different from zero.
b (Sb)
a (Sa)
( x ) = simple regression B weight
Sobel’s Z = (p=0.130)

25. Conclusion
Hypothesis 1 supported: SWB population mean for adolescents similar to adults, falling within positive range, 70-80% SM
Hypothesis 2 supported:
Mastery was a significant predictor of SWB.
Openness, conscientiousness, extraversion and neuroticism were significant predictors of SWB.

26. Conclusion Hypothesis 3 not supported:
No significant direct effect of Head Injury on SWB.
Mastery and Personality did not mediate the effect of Head Injury on SWB.

27. Conclusion
The SWB of normative adolescents is similar to the SWB of normative adults (within the 70-80% normative range).
Results have provided support for the significant effect of Mastery and Personality on SWB.
Preliminary findings suggest that individuals who have sustained previous head-injury tend to be extraverted.
It is acknowledged and noted that the validity of the measure of previous head injury is limited (i.e. obtained by self-report of adolescents). However, these findings do give some preliminary insight into the effect of head injury on SWB, and will direct the next study which is investigating the SWB of a sample of individuals hospitalised with traumatic brain injury (currently in progress).

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