fei75766_ch14_435-462.indd 445  02/06/20 01:10 PM
Chapter 14    Eysenck’s Biologically Based Factor Theory445
bimodally, distributed. Extraversion, forexample, isfairly normally distributed in
much thesame fashion asintelligence orheight. Thatis,most people arenearthe
center ofabell-shaped distribution ofextraversion. Eysenck contended thateachof
these factors meets hisfourcriteria foridentifying personality dimensions. 
First, strong psychometric evidence exists foreach, especially Factors Eand
N.ThePfactor (psychoticism) emerged laterinEysenck’s work butwasnottaken 
seriously byother researchers untilthemid-1990s (Eysenck, 1997b). Extraversion 
andneuroticism (oranxiety) arebasic factors innearly allfactor analytic studies of
human personality, including various versions oftheFive-Factor Theory (McCrae &
Costa, 1999, 2002; John &Srivastava, 1999). 
Second, Eysenck (1994a, 1994b) argued thatastrong biological baseexists for
eachofhisthree superfactors. Atthesame time, heclaimed thattraits suchasagree -
ableness andconscientiousness, which arepartofthefive-factor taxonomy (John, 
1990; W.T.Norman, 1963; Tupes &Christal, 1961), donothaveanunderlying 
biological foundation. 
Third, Eysenck’s three personality dimensions make sense theoretically. Carl
Jung(seeChapter 4)andothers haverecognized thepowerful effect onbehavior 
ofextraversion andintroversion (Factor E),andSigmund Freud (seeChapter 2)
emphasized theimportance ofanxiety (Factor N)onshaping behavior. Inaddi-
tion,psychoticism (Factor P)agrees withtheorists, suchasAbraham Maslow 
(seeChapter 9),whopropose thatpsychological health ranges from self-actualization 
(alowPscore) toschizophrenia andpsychosis (ahighPscore). 
Fourth, Eysenck repeatedly demonstrated thathisthree factors relate tosuch
social issues asdruguse(Eysenck, 1983), sexual behaviors (Eysenck, 1976), crimi -
nality (Eysenck, 1964, 1998b; Eysenck &Gudjonsson, 1989), preventing cancer and
heart disease (Eysenck, 1991c, 1991d; Grossarth-Maticek, Eysenck, &Vetter, 1988), 
andcreativity (Eysenck, 1993). 
Extraversion
InChapter 4,weexplained thatJungconceptualized twobroad personality types, 
called “extraversion” and“introversion.” Wealsonoted some differences between his
definitions andtheprevailing notion ofthese twoterms. Jungsawextraverted people 
ashaving anobjective ornonpersonalized viewoftheworld, whereas introverts have
essentially asubjective orindividualized wayoflooking atthings. Eysenck’s concepts 
ofextraversion andintroversion arecloser tothepopular usage. Extraverts arechar-
acterized primarily bysociability andimpulsiveness butalsobyjocularity, liveliness, 
quick-wittedness, optimism, andother traits indicative ofpeople whoarerewarded 
fortheirassociation withothers (Eysenck &Eysenck, 1969). 
Introverts arecharacterized bytraits opposite those ofextraverts. They can
bedescribed asquiet, passive, unsociable, careful, reserved, thoughtful, pessimistic, 
peaceful, sober, andcontrolled. According toEysenck (1982), however, theprincipal 
differences between extraversion andintroversion arenotbehavioral, butrather bio-
logical andgenetic innature.
Eysenck (1982, 1997a) believed thattheprimary cause ofdifferences between 
extraverts andintroverts isoneofcortical arousal level, aphysiological condition thatis
largely inherited rather thanlearned. Because extraverts havealower levelofcortical Final PDF to printer