Effective graphs and maps The visual display of quantitative and geographical information EPIET/EUPHEM introductory course Chris Williams, Adapted from slides Y. Hutin Communicating quantitative information • Analogue communication (graphs, maps) – Graphic overview – “hand waving” – Less precise • Digital communication (e.g. Tables) – Precise – Numeric (text also?) – Provides detailed and exact description 7:00 am Digital and analogical information Table, graph or map? (or none of the above) Vaccine coverage in Yamoussoukro district, The exact % does Ivory Coast, 1995 not add anything and may be distracting BCG 79 DTP1 75 DTP3 52 Measles 42 Y. fever 33 0 20 40 60 80 100 Coverage (%) Digital and analogical information EPIGEPS course of field epidemiology Graphs: Key areas • What is the message? – Note the singular • Choose the right graph for the right data, that demonstrates the message clearly • Style and etiquette – Message:ink ratio Decide on a message • 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 No clear message Symptom surveillance by region Two messages- too many? Weekly norovirus tests by result One message- varying proportion positive % Norovirus positive 12 10 8 6 4 2 0 13.08.12 20.08.12 27.08.12 03.09.12 10.09.12 33 34 35 36 37 Choosing the right graph 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 Histogram Urinary iodine excretion status, 24 N Parganas, West Bengal, India, 2004 Percentage 80 60 40 20 0 0-19.9 20-49.9 50-99.9 100-300 Urinary Iodine Excretion levels (µg/L) > 300 Epicurve: gastroenteritis at a music festival updated 29 July Gastroenteritis meeting case definition (n=19) Quarter 2 3 4 1 2 3 4 1 3 4 1 2 3 4 1 2 3 4 1 20-Jul 19-Jul Day quarters are of 6 hours (0:00-05:59, 06:00 - 11:59, 12:00 - 17:59, 18:00 - 23:59 ) 2 18-Jul 17-Jul 16-Jul 15-Jul Date 1 2 3 COLD/FLU CALLS: Daily ‘cold/flu’ calls as a proportion of total calls (7-day moving average) by region(2011- 2012). Presentation of time series data Proportions of a total presenting selected characteristics • Breakdown of a total in proportions: – Pie chart • Breakdown of more than one total into proportion: – Stacked bar charts adding to 100% Analog information Respiratory virus isolates by type: Pie chart Cumulated bar chart for the breakdown of many totals in proportions Proportion (%) Estimated and projected proportion of deaths due to non-communicable diseases, India, 1990-2010 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Injuries Communicable diseases Non communicable diseases 1990 2000 Year 2010 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 Lack of awareness Child sick Irregularity by health staff Lack of motivation Lack of time Lack of facility Lack of money 0% India FETP 20% 40% 60% 80% 100% Analog information Vertical bar chart: Gradient, but not quantified (No x axis) Maternal education of mothers, vaccine coverage survey, Yamoussoukro, Ivory Cost, 1995 70 Frequency (%) 60 50 40 30 20 10 0 None Prim Sec Sup Level of education EPIGEPS course of field epidemiology Analog information Prevalence of hypertension by age and sex, Aizawl, Mizoram, India, 2003 60 50 % 40 30 20 10 0 30-39 40-49 50-59 60-69 70 + Age group (years) Vertical bar chart: Quantified gradient (x Axis) Deciding the type of graph that is needed (for reference) Event followed over time? Yes! Epidemic curve? Yes! Vertical bar chart (no intervals) No! Frequency distribution? No! Line graph (Times series) Yes! Histogramme No! Break down of 1 or more totals in proportions? Yes! Only one total? Yes! Pie chart No! Is is reporting proportions in various categories? No! Juxtapozed bars cumulating to 100% Yes! Logical order in the categories? Yes! Vertical bars ranked by categories in logical order Quantified gradient x axis No! Horizontal bars ranked by magnitude of proportions No quantified gradient no x axis Putting it on the map: using maps in epidemiology Learning objectives Understand the principles of mapping Understand maps of counts and rates Understand how maps can generate hypotheses How to create maps Two basic tips • Maps in background – Include if location is relevant to your key message • Politics – Some maps/borders/ comparisons are sensitive Using maps in field epidemiology • Principals of case mapping – spot/count and population-adjusted maps • Using maps to generate hypotheses • Practical and analytic aspects of maps First, catch your hare • Where are the cases? – What do we mean by “where” • Once we know where they are, we can: – Go back to them for case management/investigation – Create a map to generate hypotheses or convey a message Geolocation Case Onset Other Case 1 24-May .... Case 2 25-May .... Case 3 26-May .... Case 4 27-May .... Case 5 28-May .... Case 6 29-May .... Case 7 30-May .... Case 8 31-May .... Case 9 01-Jun .... Case 10 02-Jun .... Case 11 03-Jun .... Case 12 04-Jun .... Case 13 05-Jun .... Case 14 06-Jun .... Case 15 07-Jun .... Geolocation Choosing a geo-locator • Cases are people (or animals!) • People move around • Options: – Place of residence (temporary residence) – Place of work or study – Healthcare provider location – Bed/room? – Merging into exposure locations e.g. Pools, water sources • Note time also – location when? General points on mapping • Two types of maps: – Spot maps – Incidence maps • Use a key • Add a title with time, place and person information Field epi map Techniques for mapping • Pen and paper • Drawing packages (including Excel) – Transparency method • Simple mapping- EpiMap, HPZone • GIS packages- ArcView, MapInfo – Can generate derived geographical variables Geographic information system (GIS) • A database linked to geographical information • Location obtained: – Directly via GPS devices or similar – Indirectly from information on address/GP/lab • Can serve as case database • Also can generate maps and test hypotheses GPS Drawing a spot map during an outbreak investigation • Rough sketch of the setting of an outbreak • One dot = One case • Other locations of potential importance are also recorded • Does not adjust for population density (OK in small places) Field epi map Using simple packages for maps: Excel SR2 02-Mar SR1 04-Mar Pedlars 01-Mar 02-Mar 02-Mar Rix Victoria Chapman 23-Feb 04-Mar 05-Mar Nursing station 14-Feb 28-Feb Spot map: ornithosis cases by place of residence, East of England 2008, n=3 Spot map: ornithosis cases by place of residence, East of England 2008 (n=10) Spot map: ornithosis cases by place of work, East of England 2008 (n=10) An incidence map adjusts for population density • List the cases • Regroup cases by location for which population denominator is available – Look up census data • Divide the number of cases by the population denominator • Choose gradients of colours to represent increasing incidence Field epi map Incidence map Invasive meningococal disease, East of England Using colours in maps • The cold / warm scale – Represents violent contrasts • Increasing density in one colour – Represents increasing levels of magnitude • Complementary colours – Use equivalent intensity – Represents unrelated notions Tips Generating hypotheses • Brainstorm likely geographical links • Map cases plus other relevant features – Water sources – Roads – Cooling towers • Can also map epidemiological indicators by area – Type of ground – Deprivation – Prevalence of another infection/disease Mapping an area exposure/determinant Q fever: incidence and spot map Take home messages • Know how to obtain geolocator information and link to cases • Use spot maps and incidence maps to generate hypotheses – Adjust for population size with rates when needed • Communicate efficiently the spatial distribution of health information • Practice map preparation to produce them rapidly when needed in practice Graph exercise: reported reasons for not swimming at Lazareto (% responses) Can't swim Too cold No swimming costume Fear of jellyfish Fear of sharks 2008 10 30 22 20 5 2009 8 34 23 24 3 2010 12 29 18 27 1 2011 9 26 19 22 7 2012 11 32 25 80 2 Questions • Message • Graph type • Style First attempt: Select, Insert graph Message: comparing proportions of responses 30 30 24 25 22 20 15 Median % response, 2008-2012 10 10 5 3 0 Can't swim Too cold No swimming costume Fear of jellyfish Fear of sharks Type: Bar chart showing proportion by category 30 Too cold 24 Fear of jellyfish 22 No swimming costume Median % response, 2008-2012 10 Can't swim 3 Fear of sharks 0 5 10 15 20 25 30 Style: reduce unnecessary ink Don’t forget the jellyfish QUESTIONS? A quick and not-so-dirty electronic map in three steps • A hardcopy of your map • A transparency • Cello tape • Permanent markers • Computer • Drawing software Tips Step 1: Place transparency on the hardcopy of map to draw map with permanent marker Tips Step 2: Stick the transparency on the screen with cello tape and follow the guide to draw map with the mouse in a drawing software Tips Step 3: Remove the transparency and edit the map in the drawing software Tips Your map is ready for use! Edit lines and fill, add title, legends and footnotes Tips Fraction of HBV infections attributable to sharps injuries among health care workers, by region, 2000 Eastern Europe Western Pacific W Europe Former USSR North America M. East S. E. Asia South Asia Gulf < 1% Latin America Africa D Africa E Australia Japan 1-9% 10-19% 20-29% 30-49% > 50% World Health Report, 2002 Tips Further functions of GIS • Point in polygon • Distance to vector (e.g. river, road) • Raster – defining exposure areas – Satellite images • ”Hotspot” maps • Interactive maps : http://www.apho.org.uk/addons/_118371/atlas.html