Catherine Mayer is the Europe editor of Time, who was part of the team who helped decide on the final list.
She said: “The proportion of women to men has risen this year and that is as a result of a deliberate editorial policy.
"The Middleton sisters are jointly on the list and the thinking behind that is that they have gone from obscurity to being among the most pictured women in the world.
“They say almost nothing so what we are talking about here is a particular kind of influence.
“It’s an influence through imagery but in the world we live in, it’s incredibly potent."
Some of Time magazine's most inflencial people of 2012
- President Barack Obama
- German leader Angela Merkel
- Nigerian President Goodluck Jonathan
- Hillary Clinton
- Billionaire investor and philanthropist Warren Buffet
- Apple CEO Tim Cook
- Samira Ibrahim, an Egyptian human rights activist
- Afghanistani women's rights advocate Maryam Durani
- Indian HIV prevention campaigner Anjali Gopalan
- The Duchess of Cambridge, and Pippa Middleton
- Lionel Messi, football player of the year
- Tennis champion Novak Djokovic
- Sarah Burton
- Tilda Swinton
- Claire Danes
- US comedian Chelsea Handler
- Viola Davis
- Internet hackers Anonymous