Discussions regarding smoothing of graphs can (and have) degenerate into fanaticism one associates with religion. I congratulate Howard in adding art and life! I tend to favor smoothing of data for graphical presentations. I will give two justifications, one practical (art?) and one theoretical (religion?). What this does for our lives is left as an exercise for the reader. Practical: --------- When discussing results, smoothed data tends to paint a "prettier picture." That is, I believe it generally allows one to see the aspects of flow data which are relevant (e.g. population positions and relative frequencies) while it ignores the aspects which tend to be irrelevant (e.g. statistical noise). I hope that most analysis packages, when doing computations on data, use the "raw" measurements and not the smoothed values for graphical output! Theoretical: ----------- In almost all cases, flow work is used to draw inferential conclusions. We are trying to classify a tumor, an individual's blood makeup, or a mechanism in a biological system. We make the assumption that the objects in the tube that we run through the flow system are representative of the "larger" population, and use tools of statistical analysis to make the inferences. Inaccurate results can, and have occurred, when this assumption isn't met. The data generated by measuring a tube in flow, is, in this sense, a sample distribution of the underlying populations. Smoothing techniques, to a large extent, are designed mathematically to give a better graphical representation of that underlying population. From this, I believe, the practical point I mentioned above follows. "Raw data" - the actual digitizations from the flow instrument, not only includes a sample of the underlying distribution, it also includes noise introduced by the instrument (I am ignoring biological preparation here). When measuring instrument performance, graphical views of this may have relevance. For most biological systems I believe it doesn't. Philosophical(??) ------------ I suppose we can draw all sorts of psychological conclusions about an individual's preference for "raw" or "smoothed" graphs. However, we should keep in mind that it is just "art" and not "life". -Marty Bigos Stanford Shared FACS Facility
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