How to counter Sivir
Let us take a look on how to beat Sivir. We will look at champions who are strong against Sivir and who are weak against Sivir. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Adc champion who counters Sivir. You can already win in champion select with the right counters for Sivir. If you want to know how to counter Sivir then you need to take into account the best picks vs Sivir and the worst picks vs Sivir. This Sivir counter data is based on matches played by Pros on patch 14.23 and previous ones. It is important to see whether Pros counter picked Sivir or whether they played as Sivir.
Champions used by Pros to counter pick Sivir
Looking at the matches from Pros (see table Pros counter picked Sivir) we can see that they picked 
Kog'Maw most often to counter pick Sivir. The matchup Kog'Maw vs Sivir occured 15 times. Sivir has 10 wins and 5 losses in this matchup. Learn how to counter pick Kog'Maw to get another perspective on the data.
Lane outcome for Sivir
When looking at Sivir 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 Sivir. The lane outcome of Sivir consists of three outcomes: Win, Loss or Draw. Let's take a look of Sivir 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 Sivir.
Conclusion
Analyze the available data and learn how to beat Sivir. To master Sivir take also a look on Sivir builds and runes for Sivir. Good luck, Summoner!