The Muggle-Born Population
In some interview, J.K. Rowling apparently said that Britain's wizarding population is roughly divided into 25% muggle-born, 50% half-blood, and 25% pureblood. However, while JKR may have said that 25% of witches and wizards are muggle-born, this is not what she has actually shown in canon.
In Harry's year at Hogwarts, there are only two confirmed muggle-born students in canon: Hermione Granger and Justin Finch-Fletchley. JKR's early class list also shows Hannah Abbott and Terry Boot as muggle-borns, but she apparently later either forgot this or changed her mind, for we learn in DH that some of Hannah's family is buried in a wizarding cemetery, and Terry was able to attend Hogwarts when Voldemort was in control. JKR originally imagined Harry's class as having 40 students, but only 30 students are ever mentioned in canon, and only 25 are mentioned elsewhere besides the sorting ceremony. 2 out of 40 students would mean that 5% of the class is definitely muggle-born. 2 out of 30 would mean that 6.66% is muggle-born. 2 out of 25 would make 8% of the class muggle-born. Any of these percentages is much lower than 25%.
(Note: Apparently I can't count, so I've had to change these percentages a few times. Hopefully they're correct now.)
Furthermore, (as far as I can remember) we only meet 3 other muggle-born students at Hogwarts: Penelope Clearwater and the two Creevey Brothers. And we only know of three muggle-borns from the previous generation: Lily Evans, Ted Tonks, and Dirk Cresswell. Again, these numbers suggest that the percentage of wizards and witches who are muggle-born is much lower than 25%
ETA: Oryx reminded me Add Mary McDonalds and the Mary who was on trial during the trio's Ministry invasion (though the two may be the same person, under her maiden and married names).
Another sign of a low percentage of muggle-borns is the WW's ignorance of muggle culture and technology. If muggle-borns were really 25% of the wizarding population, I believe that they would have had significantly more influence on wizarding culture. Wizards would have assimilated and adapted more muggle sports, muggle board games, film, television, etc.
The data I used for these calculations can be found here: https://spreadsheets.google.com/pub?hl=en&hl=en&key=0Asq6Ul6gdxBCdDlMRHoxU0NVaHA5SXQtQzRiRFI0Smc&output=html If the blood status is in parentheses, that means it was shown that way in JKR's notes, but unverified or contradicted in canon.
In Harry's year at Hogwarts, there are only two confirmed muggle-born students in canon: Hermione Granger and Justin Finch-Fletchley. JKR's early class list also shows Hannah Abbott and Terry Boot as muggle-borns, but she apparently later either forgot this or changed her mind, for we learn in DH that some of Hannah's family is buried in a wizarding cemetery, and Terry was able to attend Hogwarts when Voldemort was in control. JKR originally imagined Harry's class as having 40 students, but only 30 students are ever mentioned in canon, and only 25 are mentioned elsewhere besides the sorting ceremony. 2 out of 40 students would mean that 5% of the class is definitely muggle-born. 2 out of 30 would mean that 6.66% is muggle-born. 2 out of 25 would make 8% of the class muggle-born. Any of these percentages is much lower than 25%.
(Note: Apparently I can't count, so I've had to change these percentages a few times. Hopefully they're correct now.)
Furthermore, (as far as I can remember) we only meet 3 other muggle-born students at Hogwarts: Penelope Clearwater and the two Creevey Brothers. And we only know of three muggle-borns from the previous generation: Lily Evans, Ted Tonks, and Dirk Cresswell. Again, these numbers suggest that the percentage of wizards and witches who are muggle-born is much lower than 25%
ETA: Oryx reminded me Add Mary McDonalds and the Mary who was on trial during the trio's Ministry invasion (though the two may be the same person, under her maiden and married names).
Another sign of a low percentage of muggle-borns is the WW's ignorance of muggle culture and technology. If muggle-borns were really 25% of the wizarding population, I believe that they would have had significantly more influence on wizarding culture. Wizards would have assimilated and adapted more muggle sports, muggle board games, film, television, etc.
The data I used for these calculations can be found here: https://spreadsheets.google.com/pub?hl=en&hl=en&key=0Asq6Ul6gdxBCdDlMRHoxU0NVaHA5SXQtQzRiRFI0Smc&output=html If the blood status is in parentheses, that means it was shown that way in JKR's notes, but unverified or contradicted in canon.