Tables, graphs, and diagrams

1. Tables, graphs, and diagrams Barbara SchimmerJurmala, Latvia, 2006 Based on EPIET material

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

3. Background

4. Purpose Description Time Place Person Clinical features Comparison Odds ratios Relative risks Methods Surveillance Outbreakinvestigations Other studies:clinical epidemiologyfield trialsexperimental epidemiology Epidemiology

5. Process data Organisetriage, cleaning Summariseaggregate Explore trends relationships errors Present data Communicate Paper Poster Screenstatic  animated Use of data tables and graphics?

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

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

8. Time

9. The epidemic curve 1

10. 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

15. The arithmetic-scale line graph 1

16. 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

17. The semilogarithmic-scale line graph 1

18. 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

19. 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

20. Place

21. The one-variabletable

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

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

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

25. Person

26. The two-variable table

27. Grouped bar chart

28. Stacked bar chart

29. Component bar chart

30. 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

31. Pie chart

32. Clinical features

33. Table

34. Birth weight of 36217 newborns

35. Anything wrong with the distribution ?

36. Anything else than the relation ?

37. Comparison

38. The 2x2 table for a cohort study

39. The 2x2 table for a case control study

40. Table from a case control study

41. Design

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

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

44. Standard symbols in tables

45. Standard symbols in tables

50. 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!