research to reliably identify the prevalence, causes, and consequences of homosexuality. He first suggests that greater priority should be given to sexual arousal and attraction over behaviour and identity because it is less prone to self- and other-deception, social conditions and variable meanings. To measure attraction and arousal he proposed that biological measures should be developed and used. There are numerous biological/physiological measures that exist that can measure sexual orientation such as sexual arousal, brain scans, eye tracking, body odour preference, and anatomical variations such as digit-length ratio and right or left-handedness. Secondly, Savin-Williams suggests that researchers should forsake the general notion of sexual orientation altogether and assess only those components that are relevant to the research question being investigated. For example: To assess STIs or HIV transmission, measure sexual behaviour To assess interpersonal attachments, measure sexual/romantic attraction To assess political ideology, measure sexual identity Means of assessment Means typically used include surveys, interviews, cross-cultural studies, physical arousal measurements sexual behavior, sexual fantasy, or a pattern of erotic arousal. The most common is verbal self-reporting or self-labeling, which depend on respondents being accurate about themselves. Sexual arousal Studying human sexual arousal has proved a fruitful way of understanding how men and women differ as genders and in terms of sexual orientation. A clinical measurement may use penile or vaginal photoplethysmography, where genital engorgement with blood is measured in response to exposure to different erotic material. Some researchers who study sexual orientation argue that the concept may apply differently for men and women. A study of sexual arousal patterns found that women, when viewing erotic films which show female-female, male-male and male-female sexual activity (oral sex or penetration), have patterns of arousal which do not match their declared sexual orientations as well as men's. That is, heterosexual and lesbian women's sexual arousal to erotic films do not differ significantly by the genders of the participants (male or female) or by the type of sexual activity (heterosexual or homosexual). Men's sexual arousal patterns tend to be more in line with their stated orientations, with heterosexual men showing more penis arousal to female-female sexual activity and less arousal to female-male and male-male sexual stimuli, and homosexual and bisexual men being more aroused by films depicting male-male intercourse and less aroused by other stimuli. Another study on men and women's patterns of sexual arousal confirmed that men and women have different patterns of arousal,