I'm not even sure how you would show this. Would you look at total spending by a gender? But that could reflect income-earning differences. Would you look at percentage spent on advertising by a industry targeting a particular gender? But advertising is an arms race which one must engage in as long as the marginal return is >0, and there are all sorts of things affecting this unrelated to gullibility. Would you look at marginal return on advertising dollar split by gender? But this ought to be ~0 for both genders regardless of effectiveness, per previous.