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Agatha Christie is the best-selling novelist of all time, and her mystery books, starring detectives like Hercule Poirot and Miss Marple, have delighted readers for over 80 years. To commemorate the 125th anniversary of her birth, the UKTV channel Drama commissioned research on her work, the Telegraphreports.

After studying over 26 of Christie’s mysteries, these researchers found that most of them follow a simple formula. For example, according to the Telegraph, “The culprit was always introduced within the first half of the book, and was likely to be emotionally involved with the victim, most being spouses or blood relatives.” Here are some other interesting patterns the report found. Keep them in mind the next time you reread Murder on the Orient Express or The Murder of Roger Ackroyd.

-If there are several land vehicles in the story, the killer is likely female.

-If there a lot of nautical vehicles, the killer is likely male.

-If the victim is strangled, the murderer is probably male.

-If the setting is a country house, there is a 75 percent chance the killer is female.

-If Christie’s language is more negative, the killer is probably female.

-Female killers are typically discovered due to a domestic item, while men are normally caught using information or logic.

-If Hercule Poirot is the detective and the cause of death was stabbing, the killer will be mentioned more frequently at the beginning of the book.

-If Miss Marple is the detective, and the motive for the murder is money or an affair, the killer will be mentioned more in the later part of the novel.

In addition to these specific patterns, the researchers also found that her novels follow a similar structure in terms of plot points: First, the body will be found. Then a “closed group of characters” are introduced before detective appears.

For more on Christie’s books, head to the Telegraph.