As previously mentioned, the temporal stability of individual character traits is an important concern when personality measures are included into an empirical model. There is little doubt that personality is changing, or better developing, during childhood and adolescence (Dahmann, Anger, 2014). However, the debate on the consistency of adult personality is still ongoing. McCrae and Costa (1999) postulated that personality traits develop through childhood and are stable in adulthood – which Srivastava et al. (2003) termed plaster
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hypothesis.67 The economic literature often assumes that personality traits are constant over time and can be treated as exogenous variables (see e.g. Nyhus, Pons, 2005; Mueller, Plug, 2006; Heineck, 2011). This implies that the estimated coefficients are not biased by simultaneity or reversed causality. It is therefore of utmost importance to assure that personality measures are not affected by aging or certain life-events.
Two interpretations of trait consistency can be found in the literature: mean-level consistency and rank-order consistency (Specht et al., 2011). The first definition focusses on mean-level changes in personality trait scores of a group of individuals. Inconsistency arises if average scores of personality traits change during the life-cycle. On the contrary, the latter considers the rank-order-stability of individuals of a population. Hence, personality traits are even consistent when increases in the average scores do not change the rank-order of individuals within the group. On the other hand, the average score can remain stable but the rank-order of individuals changes when increases and decreases in certain dimensions offset each other. Costa and McCrae (1988) analysed self-reports and spouse ratings on the NEO Personality Inventory and found little evidence on the relation between personality and maturation in cross-sectional regressions. Furthermore, they detected a high retest stability of both self- reports and spouse ratings six years after the first interview. Cobb-Clark and Schurer (2012) investigated the stableness of Big Five personality traits measured by a 28-item inventory in the Australian HILDA survey. The authors concluded that personality measures were constant over time and found only little evidence that serious employment-related events influenced personality measures.
However, there exists evidence of the effect of ageing on personality. Evaluating a large North-American internet survey, Srivastava et al. (2003) detected considerable increases of conscientiousness and agreeableness of adults aged 31-60. Using data from the GSOEP and the British Household Panel Study (BHPS), Donnellan and Lucas (2008) observed age trends in Big-Five traits. Extraversion and openness were negatively correlated to age, agreeableness increased in older ages. In a more thorough study based on the GSOEP data, Specht et al. (2011) found a significant impact of age on Big-Five personality traits of participants above the age of 30. Furthermore, they investigated in how far major life events influenced personality. According to their findings, personality even predicted the occurrence of life
67 See Roberts and DelVecchio (2000) for a summary of environmental, genetic, psychological, and person- environment factors that could contribute to the increased stability of personality in adulthood.
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events which, in return, triggered changes in personality. This is related to another largely untangled problem that could derive from reserved or backward causality measuring the impact of personality on wages. Lee (2006) argued that new employees adapt to the firm culture when entering a new job. Absorbing certain memes and behavioural patterns could increase promotion perspectives and thus wages. Higher initial wages or large wage gains prospects could foster internalisation of firm values. However, it is rather questionable if behaviour in work relationships and main character traits are intertwined.
Examining the mechanisms of personality maturation of SOEP participants aged 16-82, Specht et al. (2012) detected a positive correlation between life satisfaction and positive changes in personality. Individuals reporting higher life satisfaction were less neurotic and more agreeable and conscientious. As there is strong empirical support that overall life
satisfaction and job satisfaction are closely related through spill-over effects68 from one
domain to the other (for empirical evidence see e.g. Tait et al., 1989; Judge, Watanabe, 1994; Rode, 2004), there presumably exists a relationship between personality and job satisfaction. However, the direction of causality is hitherto opaque. Roberts et al. (2006) conducted a meta- analysis of 113 samples. They demonstrated that personality traits were object to constant change, mainly in traits related to interpersonal interaction, such as socialibility and agreeableness. Yet, the changes were more robust in studies that observed individuals over a long period. Similarly, Schurer et al. (2015) found that university students became less extravert and male students from disadvantaged backgrounds became more agreeable. Yet, they did not find changes in traits related to work ethics or intellect.
Roberts and DelVecchio (2000) analysed the rank order stability of personality traits. They found that trait consistency increased from early childhood through college age until the age of 30. However, the consistency even increased to a plateau between 50 and 70. Their results support the plaster hypothesis although it contradicts the assumption that personality rarely changes above the age of 30.
With reference to the construct of locus of control, Cobb-Clark and Schurer (2011) found no meaningful changes in a four-year-period for most participants. Changes in the subjective believe of control only occurred among young and old participants. Therefore the authors suggested for both measures of personality to limit the analysis to individuals in working age. So far no study has analysed the stability of reciprocity. However, as this measure only
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reflects the reaction to good or bad behaviour of others and not the degree of altruism, it can be assumed that reciprocity should be time invariant to a large extend.
To sum up, the stability of personality is rather questionable which must be taken into consideration when interpreting the results. However, the discussed results show that personality remains rather stable for a limited period of time. Thus, despite these potential limitations, personality measures are nevertheless utilised for the following waves as the data only contains personality variables in two waves (see chapter 5.3.1 for details). Therefore, the stability of personality traits over the whole life cycle is rather irrelevant for this study. Furthermore, the sample is restricted to the working age population which eliminates potential maturation effects in retirement age.