One of them is a Pulitzer prize-winning epic running to more than 500 pages and detailing the hardships of a family of tenant farmers during the US’s Great Depression, the other is a 36-page picture book about a pink blob with an insatiable appetite.

But in a study measuring language difficulty, statisticians have analysed the text of more than 33,000 books and determined that the language used in Roger Hargreaves’s Mr Men title Mr Greedy is only marginally less complex than that used in John Steinbeck’s The Grapes of Wrath.

Quick guide The 10 hardest books measured in the study Show Hide Gulliver’s Travels (Unabridged) by Jonathan Swift – BL. 13.5 Don Quixote (Unabridged) by Miguel de Cervantes Saavedra – BL. 13.2 Ivanhoe by Walter Scott – BL. 12.9 The Legend of Sleepy Hollow and Other Stories by Washington Irving – BL. 12.7 Romeo and Juliet by William Shakespeare – BL. 12.5 Vanity Fair by William M Thackeray – BL. 12.4 Robinson Crusoe by Daniel Defoe – BL. 12.3 Frankenstein by Mary Shelley – BL. 12.2 Mansfield Park by Jane Austen – BL. 12.0 The Charterhouse of Parma by Stendhal – BL. 12.0 Photograph: Design Pics Inc/REX/Shutterstock/Rex Features

Renaissance UK, which carried out the research, uses a “readability formula” to conduct its research, analysing average sentence and word length, and word difficulty level, to pinpoint a text’s complexity. The Renaissance scale of difficulty returned scores between 0.2 and 13.5, and according to the analysis, Mr Greedy by Roger Hargreaves has a “book level” of 4.4, making it only slightly easier to read than The Grapes of Wrath, at 4.9, and the same author’s Of Mice and Men, at 4.6. Mr Greedy is ranked as harder than Roald Dahl’s The Magic Finger, at 3.1, and Fantastic Mr Fox at 4.1.

Renaissance attributes the high level for Mr Greedy to Hargreaves’ “creative use of slightly unusual words and his habit of stringing them together in long sentences”, giving the example: “Over on the other side of the table stood the source of that delicious smell. A huge enormous gigantic colossal plate, and on the plate huge enormous gigantic colossal sausages the size of pillows, and huge enormous gigantic colossal potatoes the size of beach balls, and huge enormous gigantic colossal peas the size of cabbages.”

Steinbeck, meanwhile, winner of the 1962 Nobel prize for literature, draws his fame from lines such as: “In the eyes of the people there is the failure; and in the eyes of the hungry there is a growing wrath. In the souls of the people the grapes of wrath are filling and growing heavy, growing heavy for the vintage.”

Gulliver’s Travels was the highest rated, at 13.5; while picture books Bad Bat by Laura Hambleton and No, Sid, No! by Kate Scott both have scores, at 0.2. Jojo Moyes’s tearjerker Me Before You, meanwhile, comes in at 6.8 – the same level as LEGO Star Wars: Into Battle!

Managing editor Cecelia Powell said that the “book level” rating needed to be taken in conjunction with the interest level assigned to the book by Renaissance, which considers how appropriate a book is for certain age groups.

“Our ATOS readability formula looks at how long words are, how complex sentences are – it can’t do any more than that. Then you’ve got to take into consideration the length of the book and equally important is the interest level,” she said.

With regards to Steinbeck’s low difficulty rating, “that’s why looking at the interest level we assign a book alongside its difficulty is so important – the difficulty indicates that a younger child could certainly read the words in that book, but would they be able to understand the complex themes? In no way does that book level indicate they would be able to understand them – it doesn’t take into account the literary devices used, the underlying meanings … It is just, literally, can you read the words?”

The Grapes of Wrath will interest readers aged 14 and above, Renaissance has determined, as will Of Mice and Men; Dahl’s The Magic Finger is appropriate for five- to eight-year-olds, and Mr Greedy for lower years as well.

A spokesperson for Renaissance, which provides teaching programmes for schools, said: “We do like to stress that ATOS book levels are not the only measures of the suitability of a given book for a particular student. No scientific formula can take into consideration the maturity of the themes addressed or the sophistication of the literary devices employed by the author of a book. Discretion and professional judgment are vital ingredients to successful classroom practice when guiding students to appropriate books.”