A Squib is someone who was born into a wizarding family but hasn’t got any magic powers. Kind of the opposite of Muggle-born wizards, but Squibs are quite unusual. - Chamber of Secrets
They are already extremely rare, but they will happen even in pure blood families, so I think that precludes the idea that Muggle-born wizards are more likely than not.
Some pure-blood families, such as the Blacks, disown any Squib members and remove them from their family trees, as they removed Marius Black. - Harry Potter Wiki (referencing Black family tree).
That doesn't stop some families for blaming Muggle-born wizards for a squib being born.
Some magical families would often blame any Muggle parents for a Squib's birth, as Orford Umbridge and his witch daughter would blame his Muggle wife, Ellen Cracknell, for being the fault of the son being born a Squib. - Harry Potter Wiki
Additionally the Weasley's have a second cousin who is a squib which they never talk about.
Squib's might have a better chance of producing magic born children, as in an early draft of Goblet of Fire, the second cousin had married a muggle and had a witch daughter. Perhaps that is the source of Muggle-born wizards, they are descendants of squibs who were cast out of the Magical World and their genes eventually came back into play.
tend to be born due to some wizard ancestorcare to back your claim up with any kind of data whatsoever? – n611x007 Jan 25 '17 at 10:44