First you should know that reputation only increases/decreases depending on what the voter does (upvoting/downvoting the post/comment).

There are two things that affects reputation here on Steem.

First is the reputation of the voter. 
If the reputation of the voter is higher than the votee then calculations are made. Since reputation is exponential, a higher rep user will give significant increase/decrease when upvoting a low rep account.

Second is the upvote weight given by the voter.
A 1%upvote will only give less increase to someone's reputation compared to a 100% upvote of the same level of reputation.

The same goes for downvotes.