It means to ignore the study and the results.

to toss something off can also mean to do it quickly, - I can toss that off in no time - it suggests that the task is simple (at least to the person in question), and they can dispense with it without any trouble at all. In this context it doesn't mean that they do it poorly or carelessly, just that they find it so simple, it needs little effort to complete.

It can be "invalidating the study". But it depends on the context.

What is the context? By itself, it doesn't make a lot of sense.