Stories are powerful things. They bring us in narrative form a detailed account of an event, an anecdote. Through the years we have lauded the power of a good story and rightfully so. The other side of the success of narrative has been that a story is just that, an anecdote. The power of a good story has been used for good, and for persuasion, where facts can get twisted to make an argument for one side or another. So a story has become in some corners, mere "anecdotal data," which has been deemed a bad thing. But really what has been called in to question in the quantitative milieu in which we live and work is the anecdotal datum, the singular point or event that has no sibling. A story or singular observation is just a datum, standing alone in the world.
"Data" is a Latin word and is plural, while "datum" is the singular. Like the words "curricula" (plural) and "curriculum" (singular). So a single observation is a datum, whereas multiple observations constitute data.
In terms of lesson study, the distinction that needs to be made is that a single observation may be anecdotal, but multiple observations of an event are not merely anecdotal. Multiple observations or measures constitute data. When we make our observations in a lesson study process, while the lesson is being taught, we are making numerous observations. Each observation is a singular event, but take all the observations and analyze them together: themes emerge. These themes come from multiple points of observation and transform the anecdotal datum into qualitative data.
In the research world, data tends to be divided into the realms of qualitative and quantitative data. FCAT data is quantitative; classroom observations are qualitative. Both realms of data are important and have their roles. So in a lesson study context it is important not to devalue what we see over and over again as merely anecdotal, simple because an emerging theme from multiple observations is qualitative data, a sound form of research to inform decision making.
So data collection in lesson study moves beyond the anecdotal datum into the realm of qualitative data, sound information to base our instructional decisions upon.