Nico Rosberg's Mercedes Fastest on Third Day of F1 Testing

For the second day in a row last year's Mercedes was the fastest car in Formula 1 testing at the Jerez Circuit. Yesterday, Michael Schumacher set the fastest times, and today it was Nico Rosberg. 

There are two explanations for Mercedes in last year's car setting the fastest times two days in a row. Either, Mercedes has no reason to hide because it is developing a new car. So it can let its drivers run at race speed. Or the new cars are really slower than last year's cars. 

Each day the fastest times have been about a second faster than the day before. On Tuesday, Raikkonen's fastest time was a 1m19.6. Wednesday's fastest time by Schumacher was a 1m18.5, and today's best is about another second quicker. 

What do you guys think? Are all of the other teams sandbagging to hide who is really fastest or is the lack of a blown diffuser giving a one-year-old Mercedes the advantage?

Source Autosport