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Hey there! Tawny from Moz's Help Team here.  Because of the way we index the web, we might be seeing more or fewer links going to the www version of the site you're checking than we're seeing going to the root domain. The two versions of the page can definitely have different Page Authority, and different Spam Scores.  ​ We'd recommend taking a look at both versions of the URL to see which has more spam signals headed toward it. ​I hope that helps! If you've still got questions, feel free to give us a shout over at help@moz.com.