Effective graphs The visual display of quantitative information FETP India

Competency to be gained from this lecture Present quantitative data effectively with graphs

Key areas Digital and analogical information Framing the message Choosing the right graph for the right data

Communicating quantitative information Analogical communication  Less precise  More graphic  Provides overall understanding Digital communication  Precise  Numeric  Provides detailed and exact description 7:00 am Digital and analogical information

Cases of Monkeypox by month of onset, Katako-Kombe, Zaire, Example: Digital display of information WHO-CDC Digital and analogical information

Number of cases Month of onset Cases of monkeypox by month of onset, Katako-Kombe, Zaire, FebMarAprMayJun 1996 JulAugSepOctNovDecJan 1997 Feb Secondary cases Primary cases Example: Analog display of information WHO-CDC Digital and analogical information

Do not add digital information on graphs Use graphs to communicate analogical data Addition of digital information:  Will attract the eye of some of the audience  May distract from the key analogical idea Exact figures may be provided in the script Digital and analogical information

Vaccine coverage in Yamoussoukro district, Ivory Coast, 1995 The exact % does not add anything and may be distracting EPIGEPS course of field epidemiology Digital and analogical information

Use one graph to get one idea across Don’t use a graph if there is nothing to say Frame the idea to communicate Identify the graph that matches this idea Eliminate unnecessary information If there are two ideas, use two slides Framing the message

Proportion of eligible patients whose blood slides were examined for malaria, Dhenkanal district, Orissa, Years Proportion (%) Is the graph useful?

Sources of hepatitis A virus infection among case-patients reporting at least one exposure, USA, % 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Year Proportion of cases Day care related Contact with a case Common source outbreak Foreign travel Injecting drug use Men who have sex with men Information on irrelevant risk factors Dilution of the information on injection drug use CDC

Proportion of hepatitis A cases-patients reporting injection drug use*, USA, % 2% 4% 6% 8% 10% 12% 14% Year * Among case-patients reporting at least one exposure Proportion Information on other risk factors eliminated The two waves of appear clearly in the absence of background data CDC Framing the message

Keep the ink-to-data ratio low All elements on a graph must be justified Eliminate distracting, non-essential elements  Secondary axis  Gridlines  3-D effects  Bordering lines  Etc… Framing the message

Dracunculiasis incidence Bam and Oubritenga, Burkina, Faso, Years of the project Incidence p Bam Oubritenga OCCGE Framing the message 

Frequency distribution Histogram  Graphic representation of the frequency distribution of a continuous variable  Rectangles drawn in such a way that their bases lie on a linear scale representing different intervals  Areas are proportional to the frequencies of the values within each of the intervals Epidemic curve is an example of histogram Analog information

> 300 Urinary Iodine Excretion levels (µg/L) Percentage Histogram Urinary iodine excretion status, 24 N Parganas, West Bengal, India, 2004

Cases of acute diarrhea by date of onset, Parbatia, Orissa, India (n= 41) Date of onset November 2003 Number of cases Analog information India FETP Epidemic curve

Malaria in Kurseong block, Darjeeling District, West Bengal, India, Months Incidence of malaria per 10,000 Incidence of malaria Incidence of Pf malaria Line graph for time series

Proportions of a total presenting selected characteristics Breakdown of a total in proportions:  Pie chart Breakdown of more than one total into proportion:  Juxtaposed bar charts cumulated to 100% Analog information

Road 10% Fall 32% Bites 16% Burns 7% Minor injuries 35% Types of unintentional injuries, Tiruchirappalli, Tamil Nadu, India, 2003 Incidence: 9.6 per 100 person-month (95% C.I Pie chart for the breakdown of a total in proportions

Estimated and projected proportion of deaths due to non-communicable diseases, India, % 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Year Proportion (%) Injuries Communicable diseases Non communicable diseases Cumulated bar chart for the breakdown of many totals in proportions Alignment allows comparing proportions across groups

Comparing proportions across groups No logical order: Horizontal bar chart  Sort according to decreasing proportions Logical order: Vertical bar chart  Not a continuous variable: Do not display axis  Continuous variable: Display axis Analog information

Causes of non vaccination as reported by the mothers, Bubaneshwar, Orissa, India, 2003 Analog information 0%20%40%60%80%100% Lack of money Lack of facility Lack of time Lack of motivation Irregularity by health staff Child sick Lack of awareness India FETP

Level of education Frequency (%) NonePrimSecSup Maternal education of mothers, vaccine coverage survey, Yamoussoukro, Ivory Cost, 1995 Analog information EPIGEPS course of field epidemiology Vertical bar chart: Gradient, but not quantified (No x axis)

Prevalence of hypertension by age and sex, Aizawl, Mizoram, India, 2003 Vertical bar chart: Quantified gradient (x Axis) Age group (years) %

Avoid juxtaposition of bars Juxtaposed bars charts are confusing Three options:  Eliminate one category of data if not relevant  Split the graph in two  Use cumulated bars when applicable Analog information

Number of cases Month of onset Cases of monkeypox by month of onset, Katako-Kombe, Zaire, FebMarAprMayJun 1996 JulAugSepOctNovDecJan 1997 Feb Primary cases Secondary cases The juxtaposed bars break the continuity and make it difficult to follow the dynamic of the outbreak on the graph Analog information CDC-WHO

Number of cases Month of onset Cases of monkeypox by month of onset, Katako-Kombe, Zaire, FebMarAprMayJun 1996 JulAugSepOctNovDecJan 1997 Feb Secondary cases Primary cases Cumulated bars respect the representation of the dynamic of the outbreak and illustrate the break down of cases Analog information CDC-WHO

Deciding the type of graph that is needed

Take home messages Know when you want to use a graph Know what your graph will say Tailor your graph to your message