Béla Viktor János Bartók ( ; ] ; 25 March 1881 – 26 September 1945) was a Hungarian composer, pianist and an ethnomusicologist.
 He is considered one of the most important composers of the 20th century; he and Liszt are regarded as Hungary's greatest composers .
 Through his collection and analytical study of folk music, he was one of the founders of comparative musicology, which later became ethnomusicology.
The Ego and the Id (German: "Das Ich und das Es" ) is a prominent paper by the psychoanalyst Sigmund Freud.
 It is an analytical study of the human psyche outlining his theories of the psychodynamics of the id, ego and super-ego, which is of fundamental importance in the development of psychoanalysis.
 The study was conducted over years of meticulous research and was first published in 1923.
The Dmitri Pokrovsky Ensemble (Russian: ) was founded by Dmitri Pokrovsky (1944-1996) together with his wife and life-long partner, Tamara Smyslova, in Moscow in 1973 as an experimental singing group under folk Commission of the URSS Сomposers Union.The appearance of this team completely changed in modern society the understanding and view of folklore.
 For the first time in this Ensemble came together scientific approach to the study of folklore and brilliant stage presentation of it.
 Professional musicians belonging to the city culture had to master a large number very dissimilar styles of Russian village music.
 The Pokrovsky Ensemble became the first professional groups who began to study the Russian folk music from authentic village musicians in numerous folklore expeditions.
 Participants of Pokrovsky Ensemble has been recording, learning and then performing very different traditions, styles and manners of folk singing, playing and dancing, trying to penetrate the rules of its existence, understand the laws of its development.
 Dmitri Pokrovsky was one of the first musicians who tried to bridge the gap between the old and new music.
 The credo of The Pokrovsky Ensemble that Russian traditional folk music is a living treasure of Russian culture and is the basis for all classical and contemporary Russian music.
 Pokrovsky Ensemble became the starting point in the search for new ways to stage implementation of folk music and marked the beginning of a Russian wave in the World music.
The Brisker method, or Brisker derech, is a reductionistic approach to Talmud study innovated by Rabbi Chaim Soloveitchik of Brisk, as opposed to the traditional approach which was rather holistic.
 It has since become popular and spread to yeshivas around the world.
 The Brisker method is also known as the "conceptual" approach to Talmud study, and is often referred to simply as "lomdus" (lit.
 "analytical study").
The folk music of England is traditionally based music, which has existed since the later medieval period.
 It is often contrasted with courtly, classical and later commercial music.
 Folk music has been preserved and transmitted orally, through print and later through recordings.
 The term is used to refer to English traditional music and music composed, or delivered, in a traditional style.
 English folk music has produced or contributed to several important musical genres, including sea shanties, jigs, hornpipes and dance music, such as that used for Morris dancing.
 It can be seen as having distinct regional and local variations in content and style, particularly in areas more removed from the cultural and political centres of the English state, as in Northumbria, or the West Country.
 Cultural interchange and processes of migration mean that English folk music, although in many ways distinctive, has particularly interacted with the music of Scotland.
 It has also interacted with other musical traditions, particularly classical and rock music, influencing musical styles and producing musical fusions, such as British folk rock, folk punk and folk metal.
 There remains a flourishing sub-culture of English folk music, which continues to influence other genres and occasionally to gain mainstream attention.
Contemporary folk music refers to a wide variety of genres that emerged in the mid 20th century and afterwards which were associated with traditional folk music.
 Starting in the mid-20th century a new form of popular folk music evolved from traditional folk music.
 This process and period is called the (second) folk revival and reached a zenith in the 1960s.
 The most common name for this new form of music is also "folk music", but is often called "contemporary folk music" or "folk revival music" to make the distinction.
 The transition was somewhat centered in the US and is also called the American folk music revival.
 Fusion genres such as folk rock, folktronica, and others also evolved within this phenomenon.
 While contemporary folk music is a genre generally distinct from traditional folk music, it often shares the same English name, performers and venues as traditional folk music; even individual songs may be a blend of the two.
Lloyd A. Demetrius is a mathematician and theoretical biologist at the Max Planck Institute for Molecular Genetics at Berlin, Germany, and the Department of Organismic and Evolutionary biology, Harvard University.
 He is best known for the discovery of the concept, evolutionary entropy, a statistical parameter that characterizes Darwinian fitness in models of evolutionary processes at various levels of biological organization - molecular, organismic and cultural.
 Evolutionary entropy, an analogue of the Gibbs entropy in statistical physics, is the cornerstone of directionality theory, an analytical study of evolution by variation and selection.
 The theory has applications to: a) the development of aging and the evolution of longevity; b) the origin and progression of age related diseases such as cancer, and neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease; c) the evolution of cooperation and the spread of inequality.
Turkish folk music ("Türk Halk Müziği") combines the distinct cultural values of all civilisations that have lived in Turkey and its former territories in Europe and Asia.
 Its unique structure includes regional differences under one umbrella.
 It was the most popular music genre in the Ottoman Empire era.
 After the foundation of the Turkish Republic, Atatürk asked to make a wide-scale classification and archiving of samples of Turkish folk music from around the country, which was launched in 1924 and continued until 1953 to collect around 10,000 folk songs.
 In the 1960s, Turkish folk music met with radio and folk musicians like Aşık Veysel, Neşet Ertaş, Bedia Akartürk became the most popular names of the Turkish folk music.
 In the 1970s and 1980s, with the rising popularity of arabesque and Turkish light western, Turkish folk music has lost some ground, but singers like Belkıs Akkale, İzzet Altınmeşe, Selda Bağcan, Güler Duman and Arif Sağ made successful hit songs and became important representatives of the genre.
Night music is a musical style of the Hungarian composer Béla Bartók which he used mostly in slow movements of multi-movement ensemble or orchestra compositions in his mature period.
 It is characterized by "eerie dissonances providing a backdrop to sounds of nature and lonely melodies."
Swedish folk music is a genre of music based largely on folkloric collection work that began in the early 19th century in Sweden.
 The primary instrument of Swedish folk music is the fiddle.
 Another common instrument, unique to Swedish traditions, is the nyckelharpa.
 Most Swedish instrumental folk music is dance music; the signature music and dance form within Swedish folk music is the polska.
 Vocal and instrumental traditions in Sweden have tended to share tunes historically, though they have been performed separately.
 Beginning with the folk music revival of the 1970s, vocalists and instrumentalists have also begun to perform together in folk music ensembles.

Question: What subject did the composer of night music start through his collection and analytical study of folk music?
Answer: comparative musicology