In any event, mediation is negotiation stage-managed by an independent, disinterested third party.
Arbitration has more formality than mediation.
Depending on the jurisdiction, arbitrators may be certified. There are almost no places in the world with a formal certification process for mediators. Mediation, Arbitration, and Negotiation are indeed three major kinds of 'alternative dispute resolution'. Negotiation is the process by which parties trade things of value in a civilized manner. Then someone invented lawyers, and for the past thousand years or so, we've been 'waging law' to find the right answer.