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Scatterplots (Scatter Plots)
¨ A classic type of visualization
0.2 0.4 0.6 0.8 1 1.2 1.4 0.2 0.4 0.6 0.8 1 1.2 1.4
Week 6 Video 3 Visualization Scatterplots Heat Maps Parameter - - PowerPoint PPT Presentation
Week 6 Video 3 Visualization Scatterplots Heat Maps Parameter - - PowerPoint PPT Presentation
Week 6 Video 3 Visualization Scatterplots Heat Maps Parameter Space Maps Scatterplots (Scatter Plots) A classic type of visualization 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Many say Always look at a
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Many say…
¨ Always look at a scatterplot of your data!
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But there’s a problem…
¨ Scatterplots don’t scale well to large data sets
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With lots of data points
¨ You get giant blobs
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Or if the data is not that granular
¨ You get single points hiding lots of data points
50,000 data points 5 data points
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You can increase data point size
¨ But it can be hard to display size differences
accurately
¤ 500,000 versus 5? A point 100,000 times bigger?
¨ And if data is somewhat granular, data points may
get covered
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Heat Maps
¨ Show the density of data in specific regions
Highest density Lowest density
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Heat Maps
¨ Do better with large-scale data ¨ Important to get the right box size
¤ OK to experiment a little
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Not just a substitute for scatterplots
¨ Can be used for intensity as well as density
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Example (Bowers, 2012): Color shows grade (red = poor, blue = good)
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Parameter Space Maps
¨ Important Special Case of Heat Maps ¨ Used to look at the goodness of various
parameters, particularly for BKT (Week 4)
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(Ritter et al., 2009)
¨ Proportion of skills in Cognitive Tutor where best
BKT model ends up with parameter values
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Pardos & Heffernan, 2010
¨ Analyzed the convergence of BKT models for the
EM algorithm, with different starting points
Appropriate models Degenerate models
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Next lecture
¨ State Space Networks