Consider a New user which has never rated any movie on the Website or the System has never seen the user.

How does the System recommend Movies to the User and based on what ? How will we evaluate the Recommendation , is the recommendation accurate or appropriate and how confident the system is about the Recommendation .

  • $\begingroup$ You would have to provide more information on your use case. Not all Recommender systems are equal. Are we talking about a community-based recommender or a content-based recommender? You would take a different approach based on what you're doing. $\endgroup$ Mar 8, 2018 at 16:17
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    $\begingroup$ Using a prior based on whatever scraps of info you do have; e.g., their device, location, other installed apps, etc. $\endgroup$
    – Emre
    Mar 8, 2018 at 17:46

1 Answer 1


In general, a safe default option for recommender systems is to recommend the most popular product, so two options for the recommendation:

  1. simply recommend the most popular movie in a time window around the current moment (maybe taking into account momentum),

  2. do the same but marginalizing over account info, e.g. age, gender, country, language; also, IP location is an option to get such type of info.

Confidence assessment can be done based on recommendation success rate over the results of the same recommendation to previous users with the same profile characteristics, if such data is available.

  • $\begingroup$ I don't see how you can provide an answer without asking what type of recommender they are working with. $\endgroup$ Mar 8, 2018 at 16:16
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    $\begingroup$ If the OP did not constraint the question to a specific type of recommender system, why should I ask him/her to do so instead of just suggesting valid recommendation strategies? $\endgroup$
    – noe
    Mar 8, 2018 at 16:36
  • $\begingroup$ Because, as a scientist, it is irresponsible for you to speak without having complete information. I question your judgement and methodology . . . $\endgroup$ Mar 8, 2018 at 17:21
  • $\begingroup$ That was an appropriate answer as per my requirements since i did not specify any Type or Evaluation methods such as Recall or Fscore.I wanted a General Answer.Thank you @ncasas $\endgroup$
    – m2rik
    Mar 9, 2018 at 5:14

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