1. If you recently read 50 Shades of Grey and didn’t identify with the main character
According to a study of 91 female university students published in the Psychology of Popular Media Culture, while there is no “increase in sexual behaviors or desires after reading” 50 Shades of Grey, there is “a decrease in sexual behaviors after reading the books…for those who did not identify with the main character.”
2. When you last watched a horror/ thriller movie
Dutch arousal researcher Erick Janssen, Ph.D., has found that negative emotions such as fear, anxiety and distress — which he’s produced in his test subjects by showing them horror and thriller films — contribute to greater levels of arousal. This is because, according to one theory, these emotions make one “thirst for cuddling and protection” from one’s partner. “A lot of people watch porn or pursue casual sex to cope with their negative moods,” Janssen has noted.
3. Whether or not the guy’s family is rich
A study published in the Journal of Evolutionary Psychology found that the richer the man’s family (a signal for higher income potential), the higher incidence of female orgasm.
4. The time of year
Heterosexual men report being more attracted to women’s bodies in the winter. Researchers think this is probably because there’s more novelty to female skin during the winter because it’s hidden by layers of winter clothing.
5. Whether or not your age ends in a “9”
A recent set of studies published at the Proceedings of the National Academy of Sciences indicate that we are more apt to cheat on our significant others at 29, 39, 49, etc. We’re most likely to reexamine our lives and decide we’re unsatisfied just before hitting the next decade of our lives.
6. “Coital alignment”
Sex researchers have found that the elusive simultaneous orgasm is more likely to occur with a specific sexual position called the coital alignment technique (CAT). CAT is a “modified missionary position whereby he leans his body forward until the base of his penis touches her clitoris. The partners then ‘grind’ or rock their pelvises back and forth while maintaining a constant penile-clitoral connection.” An article about CAT can be found at Ph.D. of Social Psychology Justin Lehmiller’s website.
7. How many people you’ve had sex with in the past twelve months
A July study in Social Cognitive and Affective Neuroscience found evidence that — in a number of words — people with fewer sexual partners (0-1) in the past year respond to sexual stimuli with less intensity than those with more sexual partners (2+) in the past year. So, roughly, people who sleep with others at a higher frequency are hornier than those who don’t have sex as often.
8. If you are at the gym
Psychological studies have found that physiological arousal has a part in increasing sexual arousal. People tend to misattribute their physiological arousal to the person they’re interested in, instead of the workout. For good sex, then, make sure to do it just after you worked out while watching House of 1000 Corpses.
9. If you stopped taking the pill
A study published in Psychological Science revealed that women who met their partner when they were on the pill and stopped taking it during the relationship reported less sexual satisfaction. The study did not find, however, any difference in sexual satisfaction when a woman went on the pill after entering a relationship.
10. What you do after you have sex
A study published in the Archives of Sexual Behavior that monitored the after-sex behavior of 335 participants found that higher sexual satisfaction positively correlated with more + longer duration of after-sex affection (spooning, cuddling). “Duration of after-sex affection,” notes Science of Relationships, “was even more important for sexual and relationship satisfaction than duration of sex and foreplay!” 
