In this sentence, "ne" is not necessary; however, it is recommended to put it in since your sentence expresses an "inequality". It is called the "ne expletive". It is not the negative adverb "ne pas". It is often used this way: "que+subject+ne+verb" or "qu'+subject+ne+verb ". "que+subject+ne+verb": Je l'ai appelé avant QUE VOUS NE SOYEZ partis. I called him/her before you had left. Je l'ai appelé avant que vous soyez partis. I called him/her before you had left. Both are correct, and there is no negation. "qu'+subject+ne+verb": Je l'ai appelé avant QU'IL NE SOIT PARTI. I called him/her before he had left. Je l'ai appelé avant qu'il soit parti. I called him/her before he had left. Both are correct, and there is no negation. The "ne expletive" has other uses, but in your sentence, this way is used. Hope that helps.