traue keiner Statistik, die du nicht selbst gefälscht hast

Etymology
. lit. 'do not believe any statistic that you haven't forged yourself'. While commonly attributed to, there is no proof and the proverb is completely unheard of in the English-speaking world. It was later hypothesized that the mistaken attribution was intentionally created as Nazi propaganda to discredit Churchill. The first use of this proverb is attested in 1946.

Proverb

 * 1) always take statistics with a grain of salt