Williams failed to deliver "across a number of key elements" in 2016, according to deputy team principal Claire Williams.
Since the introduction of the new power unit regulations in 2014, Williams had been very competitive, initially beating Ferrari to third place in the constructors' championship before getting the better of Red Bull to retain that position a year later.
However, 2016 has seen Williams slip back in the pecking order, with Force India beating it to fifth place in the constructors'. Williams believes there were crucial areas where the team failed to perform which need addressing ahead of next season.
"I don’t think we’ve delivered where we needed to deliver this year, across a number of key elements," Williams said. "I’m not going to go into detail on the areas of weakness we have in the team this year, but we know where those weaknesses are and we just need to make sure that we improve upon those areas over the winter.
"But Force India have done a fantastic job ... they have just done a better job than we have and we need to look into that. We don’t want to finish fifth in the world championship. It’s a bit of a disappointment having come third in two consecutive seasons, in 2014 and 2015. We just need to do a better job."
Williams will have a different driver line-up in 2017 after Felipe Massa's retirement, with rookie Lance Stroll replacing the Brazilian. Valtteri Bottas' future is also uncertain as the Finn is a target of Mercedes to replace the retired Nico Rosberg.
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