Question: How many major novels did the author write, whose 1811 book was adapted for a 2008 film with a screenplay by Andrew Davies ?

Context:
Northanger Abbey (2007 film)
Northanger Abbey is a 2007 British television film adaptation of Jane Austen's eponymous novel.
 It was directed by British television director Jon Jones and the screenplay was written by Andrew Davies.
 Felicity Jones stars as the protagonist Catherine Morland and JJ Feild plays her love interest Henry Tilney.
 The story unfolds as the teenaged Catherine is invited to Bath to accompany some family friends.
 There she finds herself the object of Henry Tilney's and John Thorpe's (William Beck) affections.
 When she is asked to stay at Northanger Abbey, Catherine's youthful and naive imagination takes hold and she begins to confuse real life with the Gothic romance of her favorite novels.
Jane Austen
Jane Austen ( ; 16 December 1775 – 18 July 1817) was an English novelist known primarily for her six major novels, which interpret, critique and comment upon the British landed gentry at the end of the 18th century.
 Austen's plots often explore the dependence of women on marriage in the pursuit of favourable social standing and economic security.
 Her works critique the novels of sensibility of the second half of the 18th century and are part of the transition to 19th-century literary realism.
Diana (TV series)
Diana is a British television drama series first broadcast by the BBC in 1984.
 It was adapted by Andrew Davies from two R. F. Delderfield novels.
Quirke (TV series)
Quirke is a British-Irish crime drama television series that was first broadcast on BBC One and RTÉ One in 2014.
 The three-part series is based on the Quirke novels by John Banville, writing under the pseudonym Benjamin Black, and was adapted by Andrew Davies and Conor McPherson.
Alfonso Bonzo
Alfonso Bonzo is a 1986 children's book by Andrew Davies and a 1990 children's television mini-series adapted from the book by the author.
 The series starred Alex Jennings as Alfonso Bonzo and Scott Riley as Billy Webb.
Brideshead Revisited (film)
Brideshead Revisited is a 2008 British drama film directed by Julian Jarrold.
 The screenplay by Jeremy Brock and Andrew Davies is based on the 1945 novel of the same name by Evelyn Waugh, which previously had been adapted in 1981 as an the television serial "Brideshead Revisited".
He Knew He Was Right
He Knew He Was Right is an 1869 novel written by Anthony Trollope which describes the failure of a marriage caused by the unreasonable jealousy of a husband exacerbated by the stubbornness of a wilful wife.
 As is common with Trollope's works, there are also several substantial subplots.
 Trollope makes constant allusions to Shakespeare's "Othello" throughout the novel.
 Trollope considered this work to be a failure; he viewed the main character as unsympathetic, and the secondary characters and plots as much more lively and interesting, but it is one of his best known novels.
 It was adapted for BBC One in 2004 by Andrew Davies as "He Knew He Was Right".
Affinity (film)
Affinity is a 2008 UK film adaptation of Sarah Waters' 1999 novel of the same name; directed by Tim Fywell and screenplay by Andrew Davies.
 The film was nominated for the GLAAD Media Award for Outstanding TV Movie or Limited Series.
Sense and Sensibility (2008 miniseries)
Sense and Sensibility is a 2008 British television drama adaptation of Jane Austen's 1811 novel "Sense and Sensibility".
 The screenplay was written by Andrew Davies, who revealed that the aim of the series was to make viewers forget Ang Lee's 1995 film "Sense and Sensibility".
 The series was "more overtly sexual" than previous Austen adaptations, and Davies included scenes featuring a seduction and a duel that were absent from the feature film.
 "Sense and Sensibility" was directed by John Alexander and produced by Anne Pivcevic.
 Hattie Morahan and Charity Wakefield star as Elinor and Marianne Dashwood, two sisters who go on "a voyage of burgeoning sexual and romantic discovery".
John Cowper Powys
John Cowper Powys ( ; 8 October 187217 June 1963) was a British philosopher, lecturer, novelist, literary critic, and poet.
 Although Powys published a collection of poems in 1896 and his first novel in 1915, he did not gain success as a writer until he published the novel "Wolf Solent" in 1929.
 He was influenced by many writers, but he has been particularly seen as a successor to Thomas Hardy, and "Wolf Solent", "A Glastonbury Romance" (1932), along with "Weymouth Sands" (1934) and "Maiden Castle" (1936), are often referred to as his Wessex novels.
 As with Hardy's novels, the landscape plays a major role in Powys's works, and an elemental philosophy is important in the lives of his characters.
 In 1934 he published his important "Autobiography".
 Powys was also a highly successful itinerant lecturer, first in England and then from 1905 until 1930 in the USA.
 Many of Powys's novels were written in America and his early novels, and all his major novels, up to and including "Owen Glendower" (1940), as well as "Autobiography," were first published in the United States

Answer: six