Making claims requires "valid" reasoning, in Buddhism… neither just promoting one's own beliefs or preferences as if they were indisputable truths, nor falling for the logical fallacy of anecdotal evidence.
This being said, many results are not validated simply because people try to show that meditation is a "quick fix" (often "8 weeks" quick) to huge difficulties. That's obviously bullsh*t: if it were this effective, this would have been known for a long time, and everybody in Asia and/or "Buddhist countries" would meditate often. Most Asians don't meditate. It's not just that monastics kept meditation techniques a secret (although some did, out of conceit, limiting the practice of laypeople to generosity (towards monastics)), it's just that the appeal of "quick fix" is very human, and meditation is not a quick fix.
If you compare meditation to hygiene (mental instead of physical), you get a better idea: physical hygiene (a bit of exercise, general cleanliness, washed ingredients for food…) is not a quick fix to diseases, yet as a long term strategy it certainly plays a major role in improved health and longer lifespan. And it's only relatively recently (at the scale of human history) that the benefits of hygiene were acknowledged.
Similarly, meditation is mental hygiene (and just like many people no longer question taking a few minutes every day for physical hygiene —from having a shower to brushing their teeth— it's beneficial to take a few minutes every day for it!) and its benefits lie in long term improvements… which is harder to study in a controlled manner, because you need to study people who say they've meditated a lot over the years but who you didn't 'control' scientifically. Yet, studies of some monastic brains suggest major impact.
by Neuroscience News:
More Rigor, Less Hype For Mindfulness and Meditation
Dependable scientific evidence has lagged worrisomely behind the rapid and widespread adoption of mindfulness and meditation for pursuing an array of mental and physical wellness goals.
The research is in Perspectives on Psychological Science. (full open access)