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!