There's no real way to know for sure. You can check the poll that Eggman pointed out. People might argue that it's not a scientific poll...which is true.
There has also been some anecdotal evidence that is concerning. There used to be a Mitsubishi technician who owned a Mirage and posted on this forum regularly. At one point, he was checking the alignment of every new Mirage that went through his dealership. At one point he had checked over 30 Mirages and ALL of them failed a rear wheel alignment check. I wasn't a statistics major but that tells me that the overall percentage of bad rear axles is likely not small.
So while we don't know the exact percentage, it's significant enough that every Mirage (2014 to present) should get an alignment check done regardless of how new the car is or even if the car "seems to drive OK." Many shops offer free alignment checks, so anyone who doesn't do this is crazy (in my opinion).
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View my fuel log 2015 Mirage ES 1.2 manual: 52.2 mpg (US) ... 22.2 km/L ... 4.5 L/100 km ... 62.6 mpg (Imp)