Have you ever wondered why, as an intelligent and educated woman who does what you are told and works hard, you are not progressing as fast as you’d like?

Girls and women are outranking boys and men more and more when it comes to education at school and university, yet that success does not generally translate into equal opportunity for women in the workplace.

According to a theory and soon-to-be-published book called the Paula Principle, developed by professor Tom Schuller, there are five factors that may be contributing to women’s current inequality and frustration.

These factors are not listed in order of importance – it will depend on a woman's "particular context, on the sector or organisation or society you live in, and what community you live in" said Schuller.

Either way, a lack of diversity in companies is costing the economy "billions of pounds".

“I have found, to an extraordinary degree, that people from all walks of life latch onto one or all of these factors and say, ‘Yeah for me, this is the one that really rings bells’ or ‘I’ve had particular experience of that one’.”

1. Discrimination, covert or overt

Whether you've experienced sexual harassment, a corporate outing to a strip club or are called "young lady” in the office, sexism is pretty common in 2017.

Schuller said there was less overt discrimination today than several decades ago, but there was "still plenty around", including when women become pregnant.

2. Structural reasons

Women are more likely to take care of their children, or look after elderly parents. Combined with the rising costs of childcare, there are various barriers which hinder women from reaching the top jobs.

Sexism debates during the Olympics Show all 5 1 /5 Sexism debates during the Olympics Sexism debates during the Olympics Helen Skelton Viewers were forced to defend Skelton after scrutiny over her outfit. BBC Sexism debates during the Olympics John Inverdale/Andy Murray Andy Murray was praised on social media for reminding the presenter about the "existence of women". This came after Inverdale called Murray 'the first person ever to win two Olympic tennis gold medals', forgetting Venus and Serena Williams have won four each. Getty Sexism debates during the Olympics Chicago Tribune This tweet from the Chicago Tribune was roundly mocked after referring to the newly crowned trap shooting bronze medallist Corey Cogdell-Unrein as 'wife of Bears lineman'. Screengrab/Twitter Sexism debates during the Olympics Katinka Hosszu After Hungarian swimmer Hosszu won the 400m individual medley, NBC were criticised for calling her husband/coach "the person responsible" for her accomplishments. Getty Sexism debates during the Olympics Alexa Moreno Viewers rallied around Mexican gymnast Alexa Moreno after she was body shamed while competing in the gymnastics. Getty

3. Psychology

It appears the old adage remains true: a woman will see one skill on a job spec that she does not feel confident about and ditch her application, while a man will apply for the same job based on the one skill that they do have.

4. Vertical network

Because the top levels of most sectors are already dominated by men, there are plenty of people that younger men can relate to and receive a helping hand from as they climb up the ladder. Schuller describes this network as “PLUs” – people like us. Sectors that are dominated by women, such as teaching and nursing, tend to be underpaid relative to other sectors.

5. Positive choices

This is the most controversial point but, as Mr Schuller said, the most interesting one to grapple with.

Men might generally cling onto the greasy pole of higher management, but women are more likely to weigh up their work/life balance.

Women will ask themselves: “Do I need the money? Do I need the status? Am I still developing in the job I’m in?”

“If the answers are no, no and yes, their choice to continue in their current role or move sideways might be sensible and rational,” he said. “Men could benefit from some of this thinking too.”

Gender pay gap

But how much positive choice means women are to blame for their own lack of upwards mobility?

Schuller replied that "everyone needs to make tradeoffs".

“I mean a genuinely positive choice,” he said. “So if it [their decision] harms them in some way, then it might not be a sensible choice.”

That does not quite answer the conundrum of a culture of presenteeism: If you take your lunch break every day, you might be less likely to get a promotion. And you’re more likely to hang around past 7pm, even if all you’re doing is liking your friend’s status on Facebook.

The actors fighting against sexism in Hollywood Show all 12 1 /12 The actors fighting against sexism in Hollywood The actors fighting against sexism in Hollywood Anne Hathaway The 32-year-old actress said she has already experiences job rejections because of her age. “Now I'm in my early thirties and I'm like, 'Why did that 24-year-old get that part? I was that 24-year-old once. I can't be upset about it, it's the way things are,” she told Glamour. EPA The actors fighting against sexism in Hollywood Helen Mirren On news that Maggie Gyllenhaal had been turned down for being ‘too old’, aged 37, to play a 55-year-old man’s partner: “It’s f***ing outrageous. It’s ridiculous. Honestly, it’s so annoying. And ’twas ever thus. We all watched James Bond as he got more and more geriatric, and his girlfriends got younger and younger. It’s so annoying.” Getty The actors fighting against sexism in Hollywood Maggie Gyllenhaal Gyllenhaal revealed she was told by a Hollywood producer that she was too old, aged 37, to play the love interest of a 55-year-old man. “It was astonishing to me. It made me feel bad, and then it made feel angry, and then it made me laugh,” she said at the time. Getty Images The actors fighting against sexism in Hollywood Meryl Streep Meryl Streep has helped fund an all-female screenwriters group called The Writer’s Lab to encourage more women to pen Hollywood scripts. She previously told Vogue in 2011: “Once women pass childbearing age they could only be seen as grotesque on some level.” Getty The actors fighting against sexism in Hollywood Emma Thompson The actress said she thought Hollywood is “still completely s***” when it comes to treating women equally to men. ““When I was younger, I really did think we were on our way to a better world. And when I look at it now, it is in a worse state than I have known it, particularly for women, and I find that very disturbing and sad.” EPA The actors fighting against sexism in Hollywood Elizabeth Banks Banks said she was driven from acting to directing due to the lack of roles for older women in Hollywood. “"[Industry sexism] drove me to direct for sure. I definitely was feeling that I was unfulfilled and a little bit bored by the things that were coming across my desk. I mean look at Gwyneth Paltrow who has her Oscar [for Shakespeare in Love] and played fifth banana to Iron Man,” she told Deadline. PA The actors fighting against sexism in Hollywood Viola Davis “I had never seen a 49-year-old, dark-skinned woman who is not a size 2 be a sexualised role in TV or film. I'm a sexual woman, but nothing in my career has ever identified me as a sexualised woman. I was the prototype of the ‘mommified’ role,” she told The Hollywood Reporter. Getty The actors fighting against sexism in Hollywood Liv Tyler The Lord of the Rings actress said she only get cast in roles where she is treated as a “second class citizen” at the age of 38. “When you’re in your teens or twenties, there is an abundance of ingenue parts which are exciting to play. But at [my age], you’re usually the wife or the girlfriend - a sort of second-class citizen. There are more interesting roles for women when they get a bit older,” she told More magazine. Getty Images The actors fighting against sexism in Hollywood Cate Blanchett The actress famously called out sexism on the red carpet at the 2014 Screen Actors Guild Awards. When a camera operator scanned her up and down, she said: “Do you do this to the guys?” In her Oscar acceptance speech for Blue Jasmine, she reminded the film industry that movies with leading women can still be successful. “And thank you to... those of us in the industry who are still foolishly clinging to the idea that female films, with women at the centre, are niche experiences. They are not -- audiences want to see them and, in fact, they earn money. The world is round, people.” Gareth Cattermole/Getty The actors fighting against sexism in Hollywood Ellen Page Asked if she had ever encountered sexism in Hollywood, Page told The Guardian: ‘Oh my God, yeah! It's constant! It's how you're treated, it's how you're looked at, how you're expected to look in a photoshoot, it's how you're expected to shut up and not have an opinion, it's how you... If you're a girl and you don't fit the very specific vision of what a girl should be, which is always from a man's perspective, then you're a little bit at a loss.” Getty Images The actors fighting against sexism in Hollywood Zoe Saldana The actress says she refuses roles where she has to play the generic girlfriend, wife or sexy bombshell. "It's very hard being a woman in a man's world, and I recognised it was a man's world even when I was a kid. It's an inequality and injustice that drove me crazy, and which I always spoke out against — and I've always been outspoken,” she told Manhattan magazine. Getty The actors fighting against sexism in Hollywood Charlize Theron The actress spoke to ELLE about negotiating equal pay for the Snow White and the Huntsman sequel: "This is a good time for us to bring this to a place of fairness, and girls need to know that being a feminist is a good thing. It doesn't mean that you hate men. It means equal rights. If you're doing the same job, you should be compensated and treated in the same way." Andreas Rentz/Getty Images

If all barriers for women are deconstructed, there will still be many people who choose a lower level job, said Schuller.

“There are lots of women who have careers and want to progress but that doesn’t mean they will become CEOS or top judges,” he said. “They want to develop in their work, but not necessarily in a vertical sense."

The main aspect of today’s culture that needs to change to bring about gender equality in the workplace, said Schuller, is scrapping the binary definitions of full-time and part-time work. The UK government's website says that a full-time worker typically works 35 hours per week.

We need to eliminate the concept that if you work part time, you are not fully committed to your career, he said.

“Things will really only open up for women in terms of roles of competence when men have mosaic careers, and they do not subscribe to this full-time pattern,” he said.