6
Correlation
¢How to find similar users?
lCheck correlation between active user’s ratings and yours
lUse Pearson correlation:
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•Generates a value between 1 and -1
•1 (perfect agreement), 0 (random)
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Similarity can also be done in terms of vector space. 
What are some ways of applying this method to this problem?
Sum of products of variances / sqrt of product of sums of variances