The Social Security Administration doesn’t combine spelling variations when compiling its annual list of popular baby names. Though this is probably the most logical way for them to present their data, it tends to skew the overall picture a bit.
For instance, according to the SSA, the top ten girl names in 2007 were Emily, Isabella, Emma, Ava, Madison, Sophia, Olivia, Abigail, Hannah and Elizabeth (in that order). If we account for spelling variations, though, the top ten is more like:
Eva could be seen as a form of Ava. That would bring Ava/Eva up to 4th place.
Hailey, the 23rd most popular girl name, can also be spelled Hailee, Hailie, Haylee, Hayley, Haylie and Hayleigh. If you throw in Haley and Haleigh as well, that brings the entire name group up to 8th place. (I tend to pronounce these last two more like Halle/Hallie, though, so I didn’t do it that way.)