“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.”

Experts have used this passage from Roger Hargreaves’ Mr Men book Mr Greedy as an example of why they have rated it as being harder to read than Roald Dahl classics such as The Magic Finger and Fantastic Mr Fox.

The ratings have been provided by statisticians and psychometricians who have examined more than 33,000 books for children and young people by scanning every page.

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“Mr Men books look really easy but they are a really high difficulty level,” says James Bell, director of professional services at Renaissance UK, which carried out the research.

Mr Men vs Roald Dahl: reading difficulty

“If you look at average sentence length and average word length and the difficulty level of the words, you can calculate the difficulty level of that book with extreme accuracy.”

The research, designed to help teachers find the correct books for pupils, rates books on a scale of 0 (easiest) to 13 (highest).

Mr Greedy is rated at 4.4 while the Dahl books The Magic Finger and Fantastic Mr Fox are rated at 3.1 and 4.1 respectively. The Twits is rated at 4.4 and Charlie and The Chocolate Factory at 4.8.

David Walliams’ books Billionaire Boy and The Boy in the Dress are rated at 4.1 and 4.2 respectively. Diary of a Wimpy Kid by Jeff Kinney is 5.2

Paul Clayton, director of NATE (National Association for the Teaching of English), said: “The language of the Mr Men books might be ‘harder’ but essentially the stories follow a simple structure and have simple resolutions and happy endings.

“Roald Dahl’s stories, on the other hand, are often more ambiguous and morally ambivalent. So whilst Dahl might be linguistically simpler, they might well be perceived to be more challenging.”

Secondary school SENCO Gemma Corby, from Hobart High School, in Norfolk, said: “I’m surprised as I know Roald Dahl was not afraid to use quite complex language in some his books (e.g. Boy), and I wouldn’t have thought Mr Men books would have required the same level of vocabulary.

“However, it is easy to fall into the trap of thinking that because a book has colourful pictures it requires a lower reading age to comprehend it.”

But Mr Bell added that guidance was sometimes needed for teachers to avoid books like John Steinbeck’s Of Mice and Men (rated at 4.6) being given to primary pupils.

He said: “Of Mice and Men has a really low reading ability but the text is complex and of an adult nature. In theory, you could give a 4.6 book to a Year 6 child but you wouldn’t want to give them it because it has content about adult themes and so on.”