CPE 619 The Art of Data Presentation

Chapter 10

The Art of Data Presentation1Overview2Types of VariablesGuidelines for Preparing Good ChartsCommon Mistakes in Preparing ChartsPictorial GamesSpecial Charts for Computer Performance Kiviat GraphsTypes of Variables3Type of computer: Super computer, minicomputer, microcomputerType of Workload: Scientific, engineering, educationalNumber of processorsResponse time of system

Guidelines for Preparing Good Charts41) Require minimum effort from the readerDirect labeling vs. legend box

2) Maximize InformationWords in place of symbols; cleary label the axes

Guidelines (contd)53) Minimize inkNo grid lines, more details

4) Use commonly accepted practicesorigin at (0,0); independent variable (cause) along x axis; the dependent variable (effect) along the y axis; linear scales; increasing scales; equal divisions5) Avoid ambiguityShow coordinate axes, scale divisions, origin;Identify individual curves and bars

Checklist for Good Graphics6Are both coordinate axes shown and labeled?Are the axes labels self-explanatory and concise?Are the scales and divisions shown on both axes?Are the minimum and maximum of the ranges shown on the axes appropriate to present maximum informationIs the number of curves reasonably small?Do all graphs use the same scale?Is there no curve that can be removed without reducing information? Are the curves on a line chart individually labeled?Are the cells in a bar chart individually labeled?Are all symbols on the graph accompanied by appropriate textural explanations?If the curves cross, are the line patterns different to avoid confusion?Are the units of measurement indicated?Is the horizontal scale increasing from left to right?Is the vertical scale increasing from bottom to top?Are the grid lines aiding in reading the curves?Does this whole chart add to information available to the reader?Are the scales contiguous?Is the order of bars in a bar chart systematic?If the vertical axis represents a random quantity, are confidence intervals shown?Are there no curves, symbols, or texts on the graph that can be removed without affecting the information?Is there a title for the whole chart?Is the chart title self-explanatory and concise?For bar charts with unequal class interval, is the are and width representative of the frequency and interval?Do the variable plotted on this cart give more information that other alternatives?Does the chart clearly bring out the intended message?Is the figure referenced and discussed in the text of the report?Common Mistakes in Preparing Charts7Presenting too many alternatives on a single chartMax 5 to 7 messages => Max 6 curves in a line charts, no more than 10 bars in a bar chart, max 8 components in a pie chartPresenting many y variables on a single chart

Common Mistakes in Charts (contd)8Using symbols in place of text

Placing extraneous information on the chartE.g., grid lines, granularity of the grid linesSelecting scale ranges improperlyAutomatic selection by programs may not be appropriate

Common Mistakes in Charts (contd)9Using a line chart in place of column chart line => continuityCPU Type8000810083008200MIPSPictorial Games10Using non-zero origins to emphasize the difference

Mine is much better than yours (emphasize difference)Mine and yours are almost the same (conceal difference)Pictorial Games (contd)11Using double-whammy graph for dramatizationUsing related metrics

Pictorial Games (contd)12Plotting random quantities without showing confidence intervals

Means of two random variablesMeans are not enough. Overlapping confidence intervals usually means that the two random quantities are statistically indifferent. Pictorial Games (contd)13Pictograms scaled by heightWrong scaling: Area(MINE) > 4*Area(YOURS)??MinePerformance = 2YoursPerformance = 1Pictorial Games (contd)14Using inappropriate cell size in histograms[0,2)[2,4)[4,6)[6,8)[8,10)[10,12)[0,6)[6,12)Response TimeResponse TimeFrequencyFrequency246810120246810120Normal distributionExponential distributionPictorial Games (contd)15Using broken scales in column charts Amplify differencesASystemResp.Time246810120BCDEFASystemResp.Time0BCDEF9101112Kiviat graphEight different metrics are plotted along eight radial lines. The metrics are: 1.CPU busy or CPU utilization HB 2.CPU only busy and none of the I/O channels LB3.CPU and channel overlap HB4.Channel only busy, CPU may be waiting for the I/O LB5.Any channel busy HB6.CPU wait LB7.CPU in problem state indicates the time used executing the users program HB8.CPU in supervisor state indicates the time spent in operating the system code. This represents the operating system overhead and is considered bad. LB17Kiviat GraphsRadial chart with even number of metricsHB and LB metrics alternateIdeal shape: star

CPUBusyCPU inSupervisor StateCPU inProblem StateCPUWaitAny ChannelBusyChannel onlyBusyCPU/ChannelOverlapCPU OnlyBusyCPU-bound system

has a high CPU utilization with very little I/O usageI/O-bound system

high I/O utilization and low CPU usagePerformance Analysis Rat Holes20ConfigurationWorkloadMetricsDetails

Reasons for not Accepting an Analysis21This needs more analysis.You need a better understanding of the workload.It improves performance only for long IOs/packets/jobs/files, and most of the IOs/packets/jobs/files are short.It improves performance only for short IOs/packets/jobs/files, but who cares for the performance of short IOs/packets/jobs/files, its the long ones that impact the system.It needs too much memory/CPU/bandwidth and memory/CPU/bandwidth isn't free.It only saves us memory/CPU/bandwidth and memory/CPU/bandwidth is cheap.See Box 10.2 on page 162 of the book for a complete listSummary22Qualitative/quantitative, ordered/unordered, discrete/continuous variablesGood charts should require minimum effort from the reader and provide maximum information with minimum inkUse no more than 5-6 curves, select ranges properly, Three-quarter high ruleKiviat Graphs show HB and LB metrics alternatively on a circular graphExercise 10.123What type of chart (line or bar) would you use to plot:CPU usage for 12 months of the yearCPU usage as a function of time in monthsNumber of I/O's to three disk drives: A, B, and CNumber of I/O's as a function of number of disk drives in a system

Exercise 10.224List the problems with the following charts