How many buyers do you need to interview to find out why you lose (and win) deals? It required some debate, but UX researchers like James Lewis and Robert Virzi ultimately convinced the UXR community that using the binomial probability formula produces the best sample size estimates....
I'm founder of Growth Velocity. We provide Win/Loss Analysis for B2B SaaS. I've led product marketing and product mgmt at startups and major companies. Also a 3X founder and CEO (one acquisition).