Let's say, we have some product in an online store, which overall rating calculates by weighted average of the following sub-ratings left by customer:
Quality ✮✮✮✮☆ Price ✮✮✮☆☆ Whatever ✮✮✮☆☆
The weight factors are: Quality - 50%, Price - 25%, Whatever - 25%
Thus, the overall rating will be:
0.8 * 0.5 + 0.6 * 0.25 + 0.6 * 0.25 = 0.7
, which is 70% of max possible rating and equals to 3.5 stars
But what if customer assessed only Quality and Price or any other combination? How to calculate weight factors correctly in such cases?