The Kinsey Scale (1948)
Developed by Alfred Kinsey from research with over 11,000 participants:
| Rating | Description |
|---|---|
| 0 | Exclusively heterosexual |
| 1 | Predominantly heterosexual, incidentally homosexual |
| 2 | Predominantly heterosexual, more than incidentally homosexual |
| 3 | Equally heterosexual and homosexual |
| 4 | Predominantly homosexual, more than incidentally heterosexual |
| 5 | Predominantly homosexual, incidentally heterosexual |
| 6 | Exclusively homosexual |
| X | No socio-sexual contacts or reactions (approaching asexuality) |
The scale was the first major scientific demonstration that sexuality is a spectrum. Its limitations are also significant: it focuses on behavior and attraction only, and does not adequately address romantic orientation, gender identity, asexuality, or non-binary genders.
The Storms Model (1979)
Michael Storms plotted hetero-eroticism and homo-eroticism on two independent axes, creating four quadrants: Heterosexual, Homosexual, Bisexual, and Asexual (low on both axes). First model to give asexuality a coherent place.
The Klein Sexual Orientation Grid (1978)
Fritz Klein's seven-variable, three-time-period grid assessing: sexual attraction, behavior, fantasies, emotional preference, social preference, self-identification, and lifestyle - each rated 1–6 across past, present, and ideal. Recognized that orientation is multi-dimensional and changes over time.
The Purple-Red Scale of Attraction (Langdon Parks, 2015)
A two-dimensional refinement of the Kinsey Scale. The horizontal axis keeps Kinsey's 0–6 rating for the direction of attraction (heterosexual to homosexual); a new vertical axis, lettered A–F, rates how attraction is experienced - from A (no sexual attraction; relationships based on friendship and/or aesthetic appreciation) through intermediate positions (e.g. romantic-only or conditional sexual interest) to F (hypersexual attraction). A person's orientation is expressed as a letter-number pair: Parks described himself as a "B0" - heteroromantic asexual. Purple was chosen as the established color of asexuality; red references "red-blooded" as an idiom for strong sexual desire. The scale's chief contribution is giving asexual and gray-asexual experiences coordinates the Kinsey Scale lacked, though like Kinsey it does not address gender identity or romantic orientation as a separate axis.
The Gender Unicorn (TSER, 2015)
Educational graphic visualizing five independent dimensions: gender identity, gender expression, sex assigned at birth, physical/sexual attraction, and emotional/romantic attraction - each as its own independent spectrum, demonstrating these axes do not determine each other.
WPATH Standards of Care
The World Professional Association for Transgender Health publishes the Standards of Care (SOC) - global best-practice guidelines for gender-affirming medical care. SOC 8 (2022) removed mandatory mental health referrals for many procedures, emphasized informed consent, and expanded guidance for non-binary and intersex people.
Biology of Sexual Orientation
Major scientific and medical bodies hold that sexual orientation results from a complex interaction of genetic, hormonal, prenatal, and other factors. Twin studies find moderate heritability. The fraternal birth order effect is robustly documented (more likely to be gay with more older brothers; attributed to maternal immune responses). Sexual orientation is not a choice, not caused by parenting, and not changeable through therapy.