Does observational data need further proof?
In many experimental fields, it is possible to "generate" a plausible amount of data and get away with it (i.e. publish the data and the conclusions in a peer reviewed journal).

Experiments need to be repeated independently. Otherwise, all sorts of things happen. Real fraud is probably the lowest number. Much more important are cases in which experiments are done without enough care or statistical methods are used in a questionable way.