public static decimal GetOwnRatingForCategory(
            this IEnumerable<ReviewFeedback> reviewFeedbacks, int userId, ReviewCategory category)
        {
            if (reviewFeedbacks == null) throw new ArgumentNullException("reviewFeedbacks");

            var assessment = reviewFeedbacks.SelectMany(fb => fb.Assessments)
                .Where(a => a.ReviewCategory.CatId == category.CatId)
                .Where(a => a.ReviewedPeer.UserId == userId && a.Reviewer.UserId == userId)
                .SingleOrDefault();

            return assessment != null ? assessment.Rating : 0;
        }
        public static decimal GetPeerRatingForPeerForCategory(
            this IEnumerable<ReviewFeedback> reviewFeedbacks, int peerId, ReviewCategory category)
        {
            if (reviewFeedbacks == null) throw new ArgumentNullException("reviewFeedbacks");

            var otherReviewersCount = reviewFeedbacks.Count(fb => fb.Reviewer.UserId != peerId);
            return otherReviewersCount > 0
                   	? reviewFeedbacks.SelectMany(fb => fb.Assessments)
                   	  	.Where(a => a.ReviewCategory.CatId == category.CatId)
                   	  	.Where(a => a.ReviewedPeer.UserId == peerId && a.Reviewer.UserId != peerId)
                   	  	.Sum(a => a.Rating)/(decimal) otherReviewersCount
                   	: 0;
        }