Absolutely, and some really weird effects show up because of human behavior and expectations during treatment. Did you know that patients think older drugs are less effective than newer ones? This is almost like a placebo effect, but people will literally not respond as well if they are being told they're getting an older drug than a newer one. How bizarre is that? You would think the efficacy would be objective since the molecules haven't changed. But I doubt any study could control for the introduction of some new treatment decades later.