Dr Caroline Leaf is a communication pathologist and self-titled cognitive neuroscientist. She is a pseudoscientist of the highest order. She once wrote a PhD. Now she has episodes of her TV show titled “Surviving cancer by using the Mind”.
This weeks edition of her newsletter started off with some subtle boasting:
“We have received many E-mails over the past years asking for Testimonies with regards to Dr Leaf’s research and teachings. We have summarized eight pages of testimonies received at TESTIMONIES. Be encouraged and feel free to refer them to friends, family, acquaintances, and work colleagues struggling with Mind issues.”
Testimonials are an empty box wrapped in shiny paper and trimmed with a bow. They look really good but offer nothing of substance. They’re simply an old advertising trick.
According to the Market Science Institute, “Testimonial solicitations – in which firms solicit consumers’ personal endorsements of a product or service – represent a popular marketing practice. Testimonials are thought to offer several benefits to firms, among them that participating consumers may strengthen their positive attitudes toward a brand, through the act of writing testimonials.” 
Who can argue with a person who says that Dr Leaf helped turn their life around? Saying anything negative just makes you sound like a cynical old boot.
And that’s the real problem, because while publishing a whole bunch of positive stories is good for marketing, it makes it very hard for those who had a genuinely bad experience to say anything. No one wants to listen to those people whom Dr Leaf has confused or mislead – it makes for terrible PR. Those people feel devalued, and sometimes worse, because it seems like everyone else had a good result from Dr Leaf’s teaching, except them.
Testimonials also make for very poor scientific evidence. Indeed, testimonials are considered the lowest form of scientific evidence . It’s all very well and good for a bunch of people to share their positive experiences, but as life changing as the experience may have been, they are not evidence of the effectiveness of Dr Leaf’s teaching. Without specific, well-designed research, no one can say if the testimonials Dr Leaf is publishing are the norm. Recent research demonstrates that self-help literature for depression may not have any benefit over a placebo treatment . So it may be that any improvement attributed to Dr Leaf’s teaching was actually the placebo effect. Dr Leaf can list testimonials until she’s blue in the face, but that doesn’t prove that her work is scientific or therapeutic.
Indeed, selectively publishing testimonials is duplicitous, telling half-truths, positively spinning her own story. How many e-mails has Dr Leaf gotten from people who have found her teaching inaccurate, ineffective, unbiblical or harmful? Dr Leaf’s social media minions deliberately delete any negative comments and block anyone from her sites that disagree with her. And over the years, many people have shared with me how arrogant and dismissive her team has been to polite, genuine concern or criticism. I can personally attest to the same treatment. If Dr Leaf was honest with her followers, she would be openly publishing the brickbats as well as the bouquets.
For her readers and followers, the testimonials need to be seen for what they are: just individual stories. Sure, we should rejoice with those who are rejoicing (Romans 12:15), and so good for those who feel Dr Leaf has helped them. But they do not constitute evidence for the therapeutic efficacy or scientific integrity of the work of Dr Leaf.
For people genuinely struggling with “mind issues”, the last thing they need is testimonials collated by Dr Leaf’s marketing team. They don’t need to be referred to Dr Leaf’s work, they need to be referred to psychologists and doctors.
And if Dr Leaf really wanted to prove her legitimacy, she would rely on independent peer-reviewed published research, not on the list of vacuous, self-serving cherry-picked testimonials that she is currently offering.
 Marketing Science Institute. Consumer Testimonials as Self-Generated Advertisements: Evaluative Reconstruction Following Product Usage. [cited 2014, Aug 3]; Available from: http://www.msi.org/reports/consumer-testimonials-as-self-generated-advertisements-evaluative-reconstru/.
 Fowler, G., Evidence-based practice: Tools and techniques. Systems, settings, people: Workforce development challenges for the alcohol and other drugs field, 2001: 93-107
 Moldovan, R., et al., Cognitive bibliotherapy for mild depressive symptomatology: randomized clinical trial of efficacy and mechanisms of change. Clinical psychology & psychotherapy, 2013. 20(6): 482-93