title: Why is Adjusted rand index(ARI) better than rand index(RI) and how to understand ARI intuitively from the formula
body: <p>I read the wikipedia article about <a href="https://en.wikipedia.org/wiki/Rand_index" rel="noreferrer">Rand Index</a> and <a href="https://en.wikipedia.org/wiki/Rand_index" rel="noreferrer">Adjusted Rand Index</a>. I can understand how they are calculated mathematically and can interpret Rand index as the ration of agreements over disagreements. But I am failing to have same intuition about ARI. </p>
  
  <p><a href="https://davetang.org/muse/2017/09/28/rand-index-versus-adjusted-rand-index/" rel="noreferrer">This blogpost</a> explains why ARI is better than RI by taking into account the chance of overlap. Can someone explain why is ARI better than RI through an example or intuitive explanation.</p>