How to give Positive or negative ratings to others responses?

I usually give positive if the response is related to the topics which i have posted.Very rarely i find irrelevant responses but never i have marked negative to anyone.I dont actually want to mark negative as i know the reputation points will go down.But yesterday i found my star rating went down from 10 to 9 and its due to some negative markings either for my topic or response.but as far as i reply i never write any irrelevant matter.But i wonder why this happened. so its you who has to decide whats to be marked for the responses you receive for your discussions

I usually give positive if the response is related to the topics which i have posted.Very rarely i find irrelevant responses but never i have marked negative to anyone.I dont actually want to mark negative as i know the reputation points will go down.But yesterday i found my star rating went down from 10 to 9 and its due to some negative markings either for my topic or response.but as far as i reply i never write any irrelevant matter.But i wonder why this happened. so its you who has to decide whats to be marked for the responses you receive for your discussions.