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well as date of birth to draw up a birth chart, typical media horoscopes are based only on aggregated birthdate ('Star' or 'Sun' sign), or year of birth (Oriental).
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4 Personality and Birthdate: Taurus, Year of the Ox, or Complete Bull? Mary E. Rogers and A. Ian Glendon

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espite widespread cynicism, many people believe in astrology — that a person’s Sun sign influences individual temperament or personality. The scientific literature on personality and astrological Sun sign published over the last four decades shows varied results. This study explored the validity of such beliefs using a balanced design incorporating age and astrological belief as covariates. One thousand, nine hundred and sixty-seven Australians aged between 28 and 51 completed a web-based survey. Personality was assessed using a 50-item version of the International Personality Item Pool (IPIP). While previous findings on age and belief in astrology were confirmed, no significant effects for the influence of either astrological Sun sign or Oriental year of birth were found.

Astrological principles, laid down around 4,000 years ago in Babylon, relate to how the sun, moon, planets and stars connect with life on earth. Some people believe that the 12 zodiac signs are associated with aspects of a person’s temperament. While most astrologers include place and time as well as date of birth to draw up a birth chart, typical media horoscopes are based only on aggregated birthdate (‘Star’ or ‘Sun’ sign), or year of birth (Oriental). Oriental astrology is based on 12-month, 12-yearly cycles, with people born in the year of a particular animal thought to reflect its qualities. Although most scientists consider it to be false (Culver & Ianna, 1988) or mystical nonsense (Pellegrini, 1973), astrology is a widespread belief system in contemporary society. The scientific literature on personality and astrological Sun sign published over the last four decades shows varied results. While some

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researchers have found a relationship between extraversion and Sun sign (Gauquelin, Gauquelin, & Eysenck, 1979, 1981; Jackson, 1979; Mayo, White, & Eysenck, 1978; Smithers & Cooper, 1978; Van Rooij, 1994; Van Rooij, Brak, & Commandeur, 1988), others found no association between astrologically derived personality profiles and scores on psychometric personality measures (Carlson, 1985; Clarke, Gabriels, & Barnes, 1996; Hartmann, Reuter, & Nyborg, 2006; Hentschel & Kiessling, 1985; Hume & Goldstein, 1977; Jackson & Fiebert, 1980; Mayes & Klugh, 1978; Russell & Wagstaff, 1983; Saklofske, Kelly, & McKerracher, 1982; Silverman & Whitner, 1974; Startup, 1985; Tyson, 1977; Veno & Pamment, 1979). Positive associations have been found between belief in astrology and high extraversion (Eliseo & Urbano, 2006; Shaughnessy, Neely, Manz, & Nystul, 1990), and with being female (Eliseo & Urbano, 2006). Searches of the scientific literature of relationships between personality characteristics and Oriental year of birth revealed one study (Dalhstrom, Hopkins, Dalhstrom, Jackson, & Cumella, 1996) that found no evidence to support any association. Inconsistencies in results from previous studies may be explained by methodological differences (e.g., personality instruments used, sample sizes, participant age, gender and belief systems and analytical techniques). To overcome limitations of past studies, for example, small and unequal sample sizes, poor statistical control of key variables such as age and selfattribution bias and in some instances lack of multivariate analysis, this study explored the relationship between personality, astrological Sun sign and Oriental calendar year of birth using a large sample size and balanced design incorporating age, gender and astrological belief as covariates. Considering Dalhstrom et al.’s (1996) recommendation, the five-factor model (FFM) of personality was selected as a widely accepted model of personality structure (Goldberg, 1993), which has been claimed to be the best account of personality ratings (Costa & McCrae, 1992b). The model uses the five dimensions of neuroticism (e.g., comprising: anxiety, anger, depression), extraversion (social, active, dominant), openness (imaginative, curious, sensitive, need for variety), agreeableness (trust, altruism, co-operation, sympathy), and conscientiousness (organised, persistent, achievement oriented). FFM dimensions have been found in many different cultures, suggesting a biological foundation for these traits (Costa & McCrae, 1992a). Gender differences in personality are constant crossnationally, with females scoring higher than males on neuroticism, openness to experience and on agreeableness (Costa & McCrae, 1992a; Feingold, 1994; Marusic & Bratko, 1998).

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While some of the variability in personality has been found to be due to developmental effects (Roberts, Robins, Trzesniewski, & Caspi, 2003; Srivastava, John, Gosling, & Potter, 2003), the genetic foundation for personality suggests that traits are relatively enduring dispositions. The genetic influence on neuroticism has been estimated at 41%, extraversion at 53%, openness to experience at 61%, agreeableness at 41% and conscientiousness at 44% (Jang, Livesley, & Vernon, 1996). A longitudinal study revealed stability coefficients of .67 for Neuroticism, .81 for Extraversion, .84 for Openness to Experience, .63 for Agreeableness and .78 for Conscientiousness (Costa & McCrae, 1992a). The present study examines the nature of any possible relationship between personality, astrological Sun sign and Oriental calendar year of birth. The main aims were to determine whether significant personality differences exist between respondent groups that: • •

share an astrological Sun sign were born in the ‘same’ Oriental year.

In both cases, the null hypothesis was that there will be no differences between groups. Further hypotheses based on the scientific literature were that: • •

extraversion is associated with belief in astrology females are more likely than males to report a belief in astrology.

Method Design

Inconsistent results in the literature prompted a number of design features for this study. While some researchers suggest that in general the five personality factors remain relatively stable in adults (Cervone & Mischel, 2002), others suggest an association between age and neuroticism (Gow, Whiteman, Pattie, & Deary, 2005) and most of the ‘Big Five’ (Srivastava et al., 2003). A restricted sample covering two complete 12-year cycles of the Oriental calendar was selected to minimise the possible impact of age upon personality. The respondent target age range was set at 28 to 51 years. This period of a person’s life generally shows the least change across the Big Five personality variables and the most consistent linear relationship (Srivastava et al., 2003). Because gender is also known to be related to some of the Big Five personality factors (Costa & McCrae, 1992a), a sample with equal numbers of male and female respondents from each astrological Sun sign and from each of the 24 Oriental years was selected.

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On the basis of previous studies, effect sizes were predicted to be small or negligible, requiring a sample size large enough to detect such an effect with power at least .8. Participants

Participants were 1,967 Australian adults (979 males, 988 females) aged 28 to 51 years (born 1954 to 1977), recruited through online methods such as a newsletter, email, and the media. Participation was voluntary and anonymous. Nearly 62% of respondents were born in the first 12year Oriental cycle, with numbers ranging between 88 and 144 for any one year, while numbers in the second 12-year Oriental cycle ranged between 57 and 67. Mean respondent age was 38.0 years (SD 6.8 years). Ages of male (mean 38.1, SD 6.8) and female (mean 38.0, SD 6.8) subsamples were practically identical. Materials

Demographic questions asked for respondent’s date of birth, gender, country of birth and current country of residence. The International Personality Item Pool (IPIP) developed by Goldberg (1999; 2006), assessed the Big Five personality variables: Neuroticism (N), Extraversion (E), Openness to experience (O), Agreeableness (A), and Conscientiousness (C). The current study used the 50-item version, consisting of 10 items for each of the Big-Five personality factors. To make each item easier to read, the word ‘I’ was added to the beginning of each statement, for example, ‘I have a vivid imagination’ and ‘I am the life of the party’. Responses were to a 5-point scale ranging from 1 (Very inaccurate) to 5 (Very accurate). Comparable with those cited in Buchanan, Johnson, and Goldberg (2005) and in Gow et al. (2005), Cronbach reliability coefficients of the five scales for this sample were: N .75, E .83, O .70, A .74 and C .79. Because of possible self-attribution bias in respect of people who believe in an astrological basis for personality (Fichten & Sunerton, 1983; Gauquelin et al., 1979, 1981; Hamilton, 1995, 2001; Synder, 1974; Van Rooij, 1994), respondents rated their belief in astrology on a 5-point Likert-type scale with responses ranging from 1 (Not at all) to 5 (Very much). Procedure

Statistical Package for the Social Sciences (SPSS) data entry builder was used to create the web-based questionnaire, which included scale button matrices and drop down lists as appropriate. Mandatory data entry ensured that all respondents returning questionnaires answered all questions. While this method may be considered to be problematic in respect

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of forcing responses to all items, on balance it was considered preferable to subsequently addressing missing data problems. While pattern and duplicate responses, outliers and respondents located outside Australia were excluded from the analysis; those born on the cusp of their Sun sign were not excluded. Appropriate adjustments were made to accommodate annual variations in the Oriental calendar year. Participants were categorised into the 12 Sun signs and 12 Oriental years according to their date of birth. To meet MANOVA assumptions and to ensure robustness of analysis (Tabachnick & Fidell, 2001), multivariate outliers were removed and cell sizes were adjusted using a random number table to ensure a gender balance for all cells in the analysis. Results

Belief in astrology was normally distributed (mean 2.87, SD 1.19) and there was a highly significant difference between males (mean 2.44, SD 1.11) and females (mean 3.31, SD 1.09), t(1963.62) = 17.49, p < .001. Females scored significantly higher than males did on all five personality variables, as shown in Table 4.1. In the basic MANOVA design the 12 Sun signs (between-subjects) and 12 Oriental years (between-subjects) were the independent variables and the scores on the five IPIP scales were the dependent variables. Because both age and belief in astrology were correlated with at least some of the personality variables, and were uncorrelated with each other, they were entered as covariates in the MANCOVA analyses. To minimise the likelihood of Type I errors, alpha was set at .01 for the multivariate analyses. There were significant correlations between all five personality variables and between the five personality variables and belief in astrology. Agreeableness, conscientiousness and neuroticism were significantly correlated with age (see Table 4.2). Table 4.1 Gender Differences on Five Personality Dimensions (Independent Samples t tests)

Personality factor

Male mean (SD)

Female mean (SD)

t1

Extraversion

32.43 (6.70)

33.83 (6.99)

–4.54

Agreeableness

34.99 (5.49)

36.96 (5.58)

–7.88

Conscientiousness

34.27 (5.95)

36.16 (6.04)

–6.97

Neuroticism

26.02 (6.79)

27.74 (7.43)

–5.35

Openness

33.79 (5.06)

34.64 (4.72)

–3.88

Note: 1 All t values are significant at p < . 001

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Table 4.2 Correlations between Five Personality Variables, Belief in Astrology and Age (N = 1967)

Variable

Age

Belief in astrology

–.00

Extraversion E

–.03

Belief

E

A

C

N

.17**

Agreeableness A

.11**

.08**

Conscientiousness C

.10**

.10**

.18** .27**

.38**

Neuroticism N

–.07**

.10**

–.38**

–.45**

–.39**

Openness

–.04

.12**

.35**

.24**

.17**

–.15**

Note:** = p < .01

Consistent with findings from the correlation analyses, both age and belief contributed significantly to the model. Main effects showed that greater age predicted higher self-reported agreeableness, F(1) = 23.82, p < .001, partial η2 .13, higher conscientiousness, F(1) = 17.93, p < .001, partial η2 .01, and lower neuroticism, F(1) = 15.17, p < .001, partial η2 .01. All power values exceeded .9. Main effects showed that belief in astrology was predicted by higher extraversion, F(1) = 52.63, p