Assume a subsistence diet, seasonally available foods, seasonal environmental conditions and a limited range of niche employment opportunities (and a sky clock/calendar). Under those circumstances, astrological birth sign would probably correlate quite well with personal health/robustness/activity preferences which would correlate quite well with what you did. Month of birth would be a good predictor (forget about the astrological sign precession etc, those are just proxies for "born in June around the time of <nutritious berry harvest>".
I don't think that astrologers are REALLY using planet positions in star-signs for prediction, those are just the traditional way of figuring out how much food and outdoors activity time you got in your first few months of existence.
Under those conditions, I would expect that birth sign->prediction would have some merit and the test of hypothesis would be that places with low seasonal variation but strong year on year variation would have "year of birth based astrology" and southern hemisphere astrology would be 6 months out of phase with northern hemisphere astrology.
None of the assumptions hold for modern Europeans. None of the predictive power of astrology would be any use at all for what to do this week (unless it was harvest/not harvest or possibly hunt/not hunt)
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