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## Tables, graphs, and diagrams

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**Tables, graphs, and diagrams**Barbara SchimmerJurmala, Latvia, 2006 Based on EPIET material**Contents**• Use of tables, graphs and graphics • Graphics in descriptive epidemiology • describe • Graphics in analytical epidemiology • compare • Designing graphics**Purpose**Description Time Place Person Clinical features Comparison Odds ratios Relative risks Methods Surveillance Outbreakinvestigations Other studies:clinical epidemiologyfield trialsexperimental epidemiology Epidemiology**Process data**Organisetriage, cleaning Summariseaggregate Explore trends relationships errors Present data Communicate Paper Poster Screenstatic animated Use of data tables and graphics?**Paper**Time unlimited Repetition Details notes? White, grey and black Screen Time < 1 min No repetition Less details Colours possible Paper vs. screen**Tables, graphics, and diagrams**• Self-explanatory • Simple! • Title (what, who, where, when) • Define abbreviations and symbols • Note data exclusions • Reference the source**The epidemic curve 2**• Histogram • Area proportional to number • No space between columns • One population • X-axis = time • Start before epidemic, continue after • Interval ≤1/4 of incubation period • Y-axis = number of cases • Usually one square = one caseEasy to make in Excel**The arithmetic-scale line graph 2**• For time series • Show actual changes in magnitude • X-axis = time • Y-axis = rate (or number) of cases • Start at 0 • Breaks possible, clearly marked**The semilogaritmic-scale line graph 2**• For time series when • interested in rate of change • X-axis = time arithmetic • Y-axis = rate (or number) of cases, logarithmic • Straight slope = constant rate of change • Steep slope = constant rapid change • Parallell lines = same rate of change • Change in slope = acceleration deceleration of rate • Start at lowest cycle, e.g. 0.1-1 or 1-10 • No breaks**In graphs...**• Labels for axes, scales and legends • Legends or keys if >1 variable • Scale divison, appropriate scale • Units of measurements in title • No grid, no numbers • No 3D**The spot map**Figure 1. Cases of meningococcal disease in Dublin 1998 by place of residence. 1 dot = 1 case**The area dot (or dot density) map**Figure 2. Cases of meningococcal disease in Dublin 1998 by area of residence. 1 dot = 1 case**The area map**Figure 3. Incidence rate (per 100,000) of meningococcal disease in Dublin 1998 by area of residence.**Bar charts**• Order • Natural • Decreasing or increasing • Vertical or horizontal • Same width of bars • Length = frequency • Space between bars and groups, but not within groups • Tables are often better**Think data-ink**Every bit of ink should have a reason**Designing graphics**• Show the data • Use ink for the data • Remove unnecessary ink • Remove gimmicks • No 3D • Careful with colours**Summary**• Use of graphics Explore and present • PresentationPaper vs screen • Description • Time - line graphs or epicurves • Place - maps or tables • Person - tables or bar charts • Clinical - tables • Analysis • Comparison - 2x2 tables, other tables • Design Save your ink!