Recommender systems mean normalization

In video about mean normalization it was shown to normalize the ratings but how is it actually good
for example if we normalize everything people that rated a movie 5 got this rating set to 2.5 and when we update new user we also made him have 2.5 for this move because that was mean of values but now he has the equality of 5 in comparison to users that actually rated it 5

Hello @Michal_Bober,

The mean is just believed to be a better guess than zero. It is also simple and intuitive. It simply assumes a new user’s preference to be on an averaged level. It is not personalised and it does not guarantee performance.

So, with such a simple trick of mean normalisation, we are able to assign an averaged rating to every movie for a new user, and this is considered an improvement.

Cheers,
Raymond