There are no reliable studies on this. And you would have to reveal what you think paid marketing is. Would that be old print, radio and TV marketing (hey these are still alive and kicking)? As to the other, I've seen others try that with ZERO effect.
Think about something carefully. Is your product that bad that you only think it will take off with a heavy marketing push as well as sales are non-existent without the effort? If you have a poor product or service, yes you can get some improvement with marketing but that's not where to spend the time, effort and money.
Can anybody tell me which one is the best marketing Technique for startup small business in present marketing scenario - Organic SEO or Paid Marketing?