A sister is a woman or a girl who shares one or more parents with another individual; a female sibling. The male counterpart is a brother. Although the term typically refers to a familial relationship, it is sometimes used endearingly to refer to non-familial relationships. A full sister is a first degree relative. Overview
The English word sister comes from Old Norse systir which itself derives from Proto-Germanic *swestēr,  both of which have the same meaning, i.e. sister. Some studies have found that sisters display more traits indicating jealousy around their siblings than their male counterparts, brothers. In some cultures, sisters are afforded a role of being under the protection by male siblings, especially older brothers from issues ranging from bullies or sexual advances by womanizers. In some quarters the term sister has gradually broadened its colloquial meaning to include individuals stipulating kinship. In response, in order to avoid equivocation, some publishers prefer the usage of female sibling over sister. Males with a twin sister sometimes view her as their female alter ego, or what they would have been like, if they had two X chromosomes. A study in Perth Australia found that girls having only youngers brothers resulted in a chastity effect, losing their virginity on average more than a year later than average. This has been hypothesized as being attributed to the pheromones in their brothers sweat and household-related errands.
This is due to hormone changes throughout their life, especially during pregnancy, where muscles around the pelvis, including piriformis muscles, tense up to stabilize the area for birth. In 2011, out of 263 patients between the ages of 45 to 84 treated for piriformis syndrome, 53.3% were female. Females are two times more likely to develop piriformis syndrome than males. Moreover, females had longer stay in hospital during 2011 due to high prevalence of the pain in females. The average cost of treatment was $29,070 for hospitalizing average 4 days. References
Further reading
Jassal, Navdeep Singh (2017). "Piriformis Muscle Syndrome". In Pope, Jason E.; Deer, Timothy R (eds.). Treatment of Chronic Pain Conditions. pp. 269–71. doi:10.1007/978-1-4939-6976-0_78. ISBN 978-1-4939-6974-6. == External links ==