Weighing scores based on participation

First of all let me apologize for my lack of math skills.
I am trying to figure out how to weigh scores based on participation rate.
Data:
4 groups of people (doesnt matter how many in each group) have the opportunity to take a test.
Each group varies in participation and average score.

Example:
Group ....... Avg Score ....... Participation Rate
Group1....... 1134............... 3%
Group2....... 1101............... 9%
Group3....... 1021............... 19%
Group4....... 1001............... 70%
Group5....... 998................. 89%

There should be a way to weigh the scores based on participation giving a more acurate "higher score"

Thanks in advance for any help

How do you want to weight this?

Does a lower participation rate deserve more reward, or vice versa?

if only 3% of a large group of people participate and get a higher score than a similarly large group with a participation rate of 89%, the slightly lower score does not seem fair does it? Punishment for larger participation needs to be negated at least somewhat.

I may actually have it now.... What do you think?
Groupx Participation% X (Overall Average % of participations X Groupx Score) = Weight
Groupx Score + Weight = new ranking score