Tables, graphs, and diagrams Barbara Schimmer Jurmala, 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

Background

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

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

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

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

Time

The epidemic curve 1

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

The arithmetic-scale line graph 1

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 semilogarithmic-scale line graph 1

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 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

Place

The one- variable table

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.

Person

The two- variable table

Grouped bar chart

Stacked bar chart

Component bar chart

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

Pie chart

Clinical features

Table

Birth weight of newborns

Anything wrong with the distribution ?

Anything else than the relation ?

Comparison

The 2x2 table for a cohort study

The 2x2 table for a case control study

Table from a case control study

Design

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

Standard symbols in tables Avereage BMI by category of weight weightmenwomen ,821, ,124, ,027, ,430, ,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

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

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!