This question has become frequent, and it touches on a couple of important points. First, the cannabinoids appear to interact, so taking pure THC or pure CBD is different from using the whole plant with its hundred cannabinoids. Second, cannabis is full of essential oils, terpenes, which are well known in herbal medicine and play a part in producing the effects of taking cannabis. Considering only the CBD:THC ratio seems a narrow way to view this question. What we do know from science is that THC becomes more stimulating as the dose goes up, and this can induce anxiety. With adequate CBD (and ?other cannabinoids) present this effect is moderated toward creativity rather than anxiety. How much CBD? There is no easy answer, and I’d say it is a matter of cautious experimentation with different ratios. Whole plant preparations may give different effects from extracts, which often lack terpenes, which is sometimes called the "entourage effect," so I would keep that in mind too.