Here is my problem:

I need a formula to calculate a score based on the number of reponses and score given for various features.

Total number of participants = 6
Total number of features = 15
Each participant rates ONLY 5 of the features, adding up to a score of 10 (Some features may not be rated at all).

My first thought (WRONG) was just to divide the sum of the scores by the number of respondents. Looked good at first, however, that was deceiving. Ex: if only 1 person rated feature A and gave it a score of 3, then the answer is 3. If 2 people rated feature B and each gave and score of 3 , then the answer would also be 3 (sum/repondents). Since 2 people rated feature B, it should clearly show more importance than feature A.

Any hints as to what the correct formula for this should be? Please.