To me a person is plus sized when they are considered 'overweight' in terms of their height/weight/bodyfat ratio. This depends on the individual and so I wouldn't call a group plus sized although its likely to be 16+ as its rare for people to achieve healthy past this as a female. I don't think plus sized models should be used in stores or online to promote clothes as it does not give out a healthy body image. I don't think models who are underweight should be used for the same reason. I think people who are a healthy size should be used - if a model is 4'11 this might be a size 4 and if a model is 6'0 this might be a size 16 or whatever.
I am a size 6/8 and I wouldn't change my size as such but I do need to get fitter and tone up as I'm 'skinny fat'. I'm only small but have a higher percentage of body fat than I should. Turning it to muscle will probably mean I go down a size but gain weight.
I think the fact the uk average is a size 16 whilst the average height is 5'5-5'7 is pretty bad and reflects the fast food and laziness culture. 9/10 people are overweight due to lifestyle choices rather than medical reasons (which is a totally different story) and need to sort themselves out. Being over weight is very bad for you and puts strain on the nhs - the same as smoking and drinking.
Does anyone use their degree?