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Channel Expressiveness and Effectiveness

Representation is how one will portray data for an audience and involves selection of right charts depending on the venue to ensure relevancy.  According to Tamara Munzner’s Visualization Analysis & Design, “Channel expressiveness dictates that it should express all of, and only, the information in the dataset attributes while effectiveness dictates the importance of attribute should match salience of the channel.”

Expressiveness fundamental simply states that ordered data should be shown in a way that our intrinsic senses as ordered and unordered data shouldn’t be shown in a way that implies ordering does exists.  Effectiveness simply states that most important attributes needs to be encoded with the most effectiveness channels for noticeability and will scale down to less effective channels with decreasing attributes.

Accuracy is critical when it comes to channel effectiveness, and we all perceived different visual channels with different levels of accuracy.  Steven’s Power law shown below is the empirical relationship between increased intensity in a physical stimulus and perceived increase in the sensation created by the stimulus. 

The ψ(I) is the magnitude of the sensation while I is the intensity of the stimulus, k is the proportionality constant on the units used, and a is the exponent that depends on the type of stimulation or sensory modality. The strongest pop out effects happen when a single item is different from other items while being identical.