经常 vs 常常 vs 常（近义词）

1)All the three words indicate frequency(with very short intervals).经常 is an adjective and can function as attributives.adverbials,etc.常常 and 常 are adverbs and only function as adverbials.Besides,经常 is formal,and the repetition happens in a rather long period of time and is regular and consistent.常 and 常常 mean"high frequency which may not be regular";they are applied to ordinary situations and are more colloquial.
2)常 is also an adjective meaning ordinary.common )eg.常理 (common sense),常人 (average people),常时 (usual time/usually)which Is not involved in the comparison here
3)In such sentences of ordinary content,all three words can be used, with 经常 being more formal.
4)The two examples above involve a rather formal content as well as a rather long period of time,therefore经常 is more suitable.Besides,经常 can also function as an attributive.
5)常 and 常常 are of different number of syllables but they are similar in terms of collocations:
6)The adiective经常has another meaning"ordinary,daily".It often functions as an attributive:⑤
7)经常 as the predicate is often put in the frame of是……的，along with 很，etc.:
8)经常 can be used in such phrases as 经常性，经常化，etc.e.g.经常性的讨论(regular liscussion),交流学习经验已经经常化了(Exchange of studying experience has become a regular practice)