You need to click on each ethnicity (on the left side of the page) which will then expand it to show the range. For example: it may say 9.5% but the range might be something like 0% to 20%.
This will also make a more detailed map come up on the right side of the page and underneath the map will be a short "history" of an area.

Also some areas overlap and you could have a parent who has Ireland and a child who shows Great Britain instead.

Ethnicity is really just an estimate or guess. The "white papers" you find on the DNA pages explain it a lot better. they can be found on the area that says "Get the most out of your ethnicity estimate".