Are there any hard statistics/industry studies supporting the use of testimonials/case studies as sales tools?

Question

For example:

1. A study by XXXXX tells us that case studies are XX% more effective than traditional advertising in engaging customers.

2. According to XXXXX, an average reader spends XX seconds on at a single page product ad, and XX minutes on a single page case study/customer success story.

Answer 1

I have no hard stats, but from my experience, a customer will spend more time on a case study than reading an ad, unless your ad has a coupon.

A coupon will be more effective than traditional advertising in engaging your customers.

You will get less activity from case studies but the case study will bring stronger clients/customers who remember you and will advertise you by word of mouth.

This is my experience from using marketing techniques in my different businesses.

I believe a mixture of regular ads, coupon ads, case studies and testimonials are necessary to reach the maximum audience.

Wishing you success and thanks for your input on my question.