How to make sense of variability
When drawing conclusions and making claims, scientists face uncertainty given the variability inherent in their data; they have to understand the sources of variability, describe patterns in light of variability, and decide when they have enough evidence.
Allowing students to experience this uncertainty and develop strategies to address it helps them to build data analysis skills in the context of meaningful science work and evaluate the basis on which scientific claims are made.
A closer look at uncertainty in the classroom
In some of the implementations of the vials investigation in fifth grade classrooms, more measurement errors or issues with scales lead to more variability in the weight data. Students work with this uncertainty through:
Discussing and disagreeing about claims
Implementing strategies to increase their confidence in the data.
Discussing and disagreeing about claims
Student ideas include:
“It is likely that water stays the same weight because most of the vials stayed the same weight.”
“Why did some of the vials go up or down?”
“Some things might have melted before you got to weigh it.”
“Maybe our scales weren’t working right.”
“What makes you think it decreased? Why did you leave out one class’s data?”
“Maybe for some reason it (the weight) could go up or down, but from looking at this it is much more likely that it stays the same.”
One group combined the two classes’ data and concluded that the weight of water does not change.
One group found the data too different and only focused on the class’s data that supported their ideas.
Implementing strategies to increase confidence in the data
Strategies teachers and students have agreed on include:
Asking another class for their data to draw conclusions from based on more cases
Comparing the weights two different scales provide for the same objects to test if one is faulty
Retesting while implementing strategies to reduce error (spilling, leaning against the scale)
Researching to see what other scientists have found
Instructional moves to support this form of uncertainty
Allow students to discuss the reasons that results might vary.
Talk to students about how this kind of uncertainty is always a part of science– scientists can’t test every single (vial, seed) in the world and have to decide when they are sure enough. Provide examples of when scientists have decided they needed more information to be sure (for example, to be sure a treatment is safe).
If possible, allow students to consider how to increase their precision and re-test if they are bothered by results. This is more useful at this age than labeling mistakes as measurement error and having them explain why they did not get the “right answer.”
