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Tables, graphs, and diagrams Barbara Schimmer Jurmala, Latvia, 2006 Based on EPIET material

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Contents Use of tables, graphs and graphics Graphics in descriptive epidemiology °describe Graphics in analytical epidemiology °compare Designing graphics

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Background

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Epidemiology Purpose Description °Time °Place °Person Clinical features Comparison °Odds ratios °Relative risks Methods Surveillance Outbreak investigations Other studies: clinical epidemiology field trials experimental epidemiology

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Use of data tables and graphics? Process data Organise triage, cleaning Summarise aggregate Explore °trends °relationships °errors Present data Communicate Paper Poster Screen static animated

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Paper vs. screen Paper Time unlimited Repetition Details notes? White, grey and black Screen Time < 1 min No repetition Less details Colours possible

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Tables, graphics, and diagrams Self-explanatory Simple! Title (what, who, where, when) Define abbreviations and symbols Note data exclusions Reference the source

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Time

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The epidemic curve 1

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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 case Easy to make in Excel

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The arithmetic-scale line graph 1

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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

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The semilogarithmic-scale line graph 1

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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

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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

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Place

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The one- variable table

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The spot map Figure 1. Cases of meningococcal disease in Dublin 1998 by place of residence. 1 dot = 1 case

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The area dot (or dot density) map Figure 2. Cases of meningococcal disease in Dublin 1998 by area of residence. 1 dot = 1 case

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The area map Figure 3. Incidence rate (per 100,000) of meningococcal disease in Dublin 1998 by area of residence.

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Person

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The two- variable table

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Grouped bar chart

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Stacked bar chart

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Component bar chart

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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

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Pie chart

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Clinical features

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Table

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Birth weight of 36217 newborns

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Anything wrong with the distribution ?

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Anything else than the relation ?

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Comparison

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The 2x2 table for a cohort study

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The 2x2 table for a case control study

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Table from a case control study

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Design

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Think data-ink Every bit of ink should have a reason

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Designing graphics Show the data Use ink for the data Remove unnecessary ink Remove gimmicks No 3D Careful with colours

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Standard symbols in tables Avereage BMI by category of weight weightmenwomen 40-49 -. 50-5919,821,8 60-6923,124,8 70-7925,027,6 80-8927,430,5 90-9929,834,2 explanation of symbols - = we measured, no case in this category, we can´t say that it is 0. = we measured, but we cant calculate the average of 1 case

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Standard symbols in tables Cause specific mortality Cause of deathmenwomen CVD5035 Pneumonia4530 CA prostatae10x CA cervicis uterix10 explanation of symbols x = not displayed for logical reasons

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Summary Use of graphicsExplore 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 DesignSave your ink!

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