How to counter Zed
Let us take a look on how to beat Zed. We will look at champions who are strong against Zed and who are weak against Zed. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Mid champion who counters Zed. You can already win in champion select with the right counters for Zed. If you want to know how to counter Zed then you need to take into account the best picks vs Zed and the worst picks vs Zed. This Zed counter data is based on matches played by Pros on patch 14.9 and previous ones. It is important to see whether Pros counter picked Zed or whether they played as Zed.
Champions used by Pros to counter pick Zed
Looking at the matches from Pros (see table Pros counter picked Zed) we can see that they picked 
Ahri most often to counter pick Zed. The matchup Ahri vs Zed occured 20 times. Zed has 11 wins and 9 losses in this matchup. Learn how to counter pick Ahri to get another perspective on the data.
Lane outcome for Zed
When looking at Zed counters you will notice that win rates alone are not conclusional. Therefore we provide an overview (see table Lane Outcome) where you can see the lane outcome of Pros who played Zed. The lane outcome of Zed consists of three outcomes: Win, Loss or Draw. Let's take a look of Zed lane and match outcome for specific matchups. Considering the lane outcome and the match outcome of a specific matchup, might enable you to find the right counter for Zed.
Conclusion
Analyze the available data and learn how to beat Zed. To master Zed take also a look on Zed builds and runes for Zed. Good luck, Summoner!