Determining if a word is an anagram of another

The question was to see if a word is an anagram of another word.

How would you improve this? It returns True if an anagram, or False otherwise.

# write the function is_anagram
def is_anagram(test, original):
    if len(test) != len(original):
        return False
    for letter in test.lower():
        if letter not in original.lower():
            return False
    for letter in original.lower():
        if letter not in test.lower():
            return False
    return True

You need to check if each letter occurs the name number of times in both strings.

One method would be to sort the letters and compare the lists of letters for equality.

Here is my approach:

def is_anagram(test, original):
  return sorted(list(test.lower())) == sorted(list(original.lower()))

This algorithm is far from optimal runtime O(n*logn), but I have chosen it because of its simplicity.
For an Efficient algorithm see the comment of @corsiKa for a quite simple O(n) algorithm.

StackExchange Code Review Q#96475, answer score: 13