
Image above captured from Hansoft (www.hansoft.se)
Of all of the concepts in Scrum, one of the most maligned (anecdotally it would seem, at least) is the Story Point. I have heard Scrum’s proponents and detractors alike discount the idea, saying Story Points are meaningless or too abstract, and that estimates and forecasts are better served by Ideal Days. For me, it’s a matter of probability, and the argument between Ideal Days and Points is one between precision and accuracy.
An example: imagine a man who weighs exactly 215.68 pounds. If you put that man on a calibrated digital scale, you will see that he, indeed, weighs 215.68 pounds, a number that is both accurate and precise. But, what if you didn’t have that scale and you instead had to look at the man and simply estimate his weight?
If you said he weighs between 150 and 160 pounds, you would be neither accurate nor precise. If you said he weighs 208.667 pounds you would be precise, but not accurate. But, if you instead said that he weighs between 210 and 220 pounds, you wouldn’t be precise, but you would be accurate. And if I have to choose between accuracy and precision, I’ll take accuracy every time. There’s a reason you hunt quail with a shotgun and not a 9mm. Continue reading →