Let's assume that we have 2 people and 5 objects with the following ratings (scale 1-5):
John has rated obj1:5, obj2:1 , obj3:(unknown value), obj4:2 , obj5:2 and Jack has rated obj1:1, obj2:5 , obj3:2, obj4:5 , obj5:5. Do i need obj3:2 when calculating the mean of Jack's ratings or just hypothetically delete it and use the other objects that have been rated by both of them? I want to calculate Pearson correlation between John and Jack. Also, i know that the obj3 will not be used in Pearson correlation function.
Thank you for your time.