STDEV to measure movie ratings

Question

I'm looking at movie ratings across a friend group and I'm trying to find the best way to measure how people rate movies compared to IMDb ratings.

Here you can see my table titled fRating, which is a fact table that contains the MovieID, the RaterID, and their UserRating:

This joins with dMovies, which is the dimension table for all of the movies. That table is shown below:

Now, how would I go about finding how much each rater varies from the IMDb ratings? Here is my attempt, using STDDEV:

SELECT a.[RaterID]
      ,Rater
      ,STDEV(([UserRating] - ROUND(b.IMDb_Rating,0))) as StdDev

  FROM [IMDbRatings].[dbo].[fRating] a
    JOIN [IMDbRatings].dbo.dMovies b ON a.MovieID = b.MovieID
    JOIN [IMDbRatings].dbo.dRaterID c ON a.RaterID = c.RaterID
  GROUP BY a.RaterID, Rater

Here are the results that I get from that:

Am I on the right track? Is this doing what I want it to do?

Thank you for your wisdom!