When I meet my friend Emily, 40, for coffee, the conversation turns to children. I'm 41 and don't have any, but she has three - Molly, eight, Addie, five, and Freddie, two.
She talks about the catastrophes of the week.
Molly has started taking Emily's make-up, without asking. Freddie has suddenly decided to start flinging his dinner at the wall. But Addie is filling up her star charts at school and practising her reading skills on her brother - and she's doing well in her swimming lessons.
'So, Addie is the favourite then?' I tease, expecting Emily to roll her eyes and protest in horror. Instead, she drops her gaze and turns away from me. 'Yeah,' she says, quietly. 'I know it's a terrible thing to say, but I can enjoy being her mum. It's constant chaos with the other two.'
I'm shocked to hear Emily admit this, but I'm not entirely surprised. When there's more than one child in a family, there's always going to be some competition - whether it's for love, attention or success.
Actress Maggie Gyllenhaal last week revealed she had been 'envious' of her younger brother Jake at the start of her career, worrying there wouldn't be 'enough room' for both in Hollywood. She told the New York Times: 'I don't think I was in touch with the envy, but it was there.'
As the eldest of six girls, I know how that envy feels. I've always been pretty sure there's a favourite in my family - and it isn't me.
My parents have always said they love us all equally, no matter how hard we've tried to trick them into admitting that one of us has 'favourite' status. But the rest of us are convinced that Grace, one of the middle two, is the favourite sister.
Like Emily's daughter Addie - another middle child - Grace gave our parents an easy ride. As well as excelling academically, she won debating competitions and art prizes and took several starring roles in school plays.
Her excellence continues into adulthood. She has two delightful little boys, a beautiful home and is brilliant at cooking. Most of all, she makes every triumph and achievement look incredibly easy. She glides like a swan, while the rest of us fail and thrash about.
Unlike the other girls - me, Beth, Liv, Maddy and Dotty - I don't think Grace ever had to be picked up drunk from a terrible teenage party. She never came home with an unsuitable boyfriend. She's never worn an outfit that has prompted the words: 'You're not going out like that!' If she was my daughter, she'd probably be my favourite.
Last year, research published by Alexander Jensen in the Psychological Bulletin journal found that parents tended to favour children who were 'conscientious, responsible and organised'.
It makes sense to me. Parenting is challenging and, as a mother, you're going to be more well- disposed towards the child who doesn't seem to be going out of their way to create extra trouble.
But having a soft spot for one can lead to problems.
Researchers in China have found a link between parental favouritism, poor sibling relationships and mobile phone addiction in teenagers. And in a Canadian study, seven out of eight homeless teenagers in Toronto told researchers that there was a 'golden child' in the family, and it wasn't them.
If you believe your brother or sister is the favourite, it's going to have an impact.
I realise my parents always did their very best to make sure that my sisters and I had everything we needed - and we all had different needs at different times.
But when I was growing up, I was preoccupied with fairness. My younger sisters seemed to be granted more freedom at a younger age than I had been. It was difficult to be the eldest since it felt like I was constantly being told I should be setting a better example for my siblings.
Grace didn't seem to need anyone to show her the way. She seemed to get everything right immediately. I constantly compared myself with her. Trying to keep up with my little sister has left me with a tremendous drive, which has been a blessing and a curse. I'm fiercely ambitious and determined to achieve great things in my career - but deep down, I don't feel as though I'll ever have achieved enough.
J. Jill Suitor, a professor of sociology at Purdue University in the US, conducted a 25-year study on parental favouritism which found career accomplishments did little to improve your standing in your parents' eyes.
O ver the years I've written four bestsellers. But every time I publish a novel I wonder if I'll have the chance to be the favourite for a week or so. This hasn't happened yet - and now I know why.
My mother never hugged me. And her cruel response when my sister got meningitis still haunts us.
Happily, as we've all grown up, my sisters and I have become closer than we were as children. We understand how much pressure our parents were under when they were raising us—as well as how much pressure we put ourselves under. Grace still feels sensitive about her 'favourite' status and has worked very hard to stop pushing herself to maintain impossible standards.
The rest struggle with perfectionism. We're trying to be grown-up about it, but we're also still trying to 'do a Grace' and get a Blue Peter badge. Other people aren't so lucky. Emily is also one of three, and her baby brother is the family favourite. 'It's become harder to ignore it now that we all have kids,' she says. 'I could laugh it off when we were younger, but my parents clearly favour his children over mine, giving them lavish presents and taking them on holiday. Worse, they'll shout at my kids for knocking over a glass or climbing over a sofa - but his lot seem to get away with it.
'It makes me resent my brother, and I think it's stopped me from having a closer relationship with him. My sister and I tried to discuss it with him, but he's not interested. My sister and I bond over the problem and leave him out, and I think that makes the situation worse.'
For most of my life, I've struggled with comparison, feeling bad about myself because everyone else seems to be doing so much better than me. I've realised that I've been scrolling through Instagram as though it's a family photo album, looking at the accomplishments of my peers and feeling something akin to sibling envy. Now I realise this is probably connected with the way I grew up. It wasn't just my parents who compared my sisters and me; everyone did. So I learned to compare myself with other people to try to understand who I am and how I'm doing.
But now we're older, I focus on my similarities with my sisters and our points of connection.
When we were all growing up in the same house, my envy and anxiety were difficult to deal with. Now we’re adults; we maintain nourishing friendships.
Maggie Gyllenhaal says time has improved her relationship with Jake too. ‘We’ve never been as close as we are now,’ she says. ‘We’re finally, maybe in the last five years, more and more and more even each day really interacting.’
Ultimately, my quest to find out more about family favouritism has shown me that it doesn’t matter whether there was really a favourite in the family. If you feel that one of your siblings has been chosen over you, it’s going to have an impact on the way you show up in the world.
For me, that means I’m always going to be trying a little bit too hard. But I’m grateful for my drive and everything it brings me. Maybe I’ll never be anyone else’s favourite, but I can choose myself.
Some names and identifying details have been changed.