grammar - Comparing ということだ and そうだ

天気予報【てんきよほう】によると今年【ことし】の夏【なつ】はあついだろう(ということだ/そうだ)

Both ということだ and そうだ can represent an 'externally induced' opinion/conclusion.
How do we identify the context to choose one over the other then?

Answer

There are two main differences:

1. 
   

   「ということだ」 conveys more certainty in the information than 「そうだ」 does.

   
   


2. 
   

   「ということだ」 indicates that the information was heard from a public source, while 「そうだ」 indicates that it was heard from a private source (e.g., your friends or family).