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Effective graphs and maps The visual display of quantitative and geographical information EPIET/EUPHEM introductory course Chris Williams, Adapted from.

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Presentation on theme: "Effective graphs and maps The visual display of quantitative and geographical information EPIET/EUPHEM introductory course Chris Williams, Adapted from."— Presentation transcript:

1 Effective graphs and maps The visual display of quantitative and geographical information EPIET/EUPHEM introductory course Chris Williams, Adapted from slides Y. Hutin

2 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

3 Table, graph or map? (or none of the above)

4 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

5 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

6 Decide on a message Dont 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

7 No clear message Symptom surveillance by region

8 Two messages- too many? Weekly norovirus tests by result

9 One message- varying proportion positive

10 Choosing the right graph

11 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

12 > 300 Urinary Iodine Excretion levels (µg/L) Percentage Histogram Urinary iodine excretion status, 24 N Parganas, West Bengal, India, 2004

13 Epicurve: gastroenteritis at a music festival

14 COLD/FLU CALLS: Daily cold/flu calls as a proportion of total calls (7-day moving average) by region( ). Presentation of time series data

15 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

16 Respiratory virus isolates by type: Pie chart

17 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

18 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

19 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

20 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)

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

22 Deciding the type of graph that is needed (for reference)

23 Putting it on the map: using maps in epidemiology

24 Learning objectives Understand the principles of mapping Understand maps of counts and rates Understand how maps can generate hypotheses How to create maps

25 Two basic tips Maps in background –Include if location is relevant to your key message Politics –Some maps/borders/ comparisons are sensitive

26 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

27 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

28 Geolocation CaseOnsetOtherGeolocation Case 124-May.... Case 225-May.... Case 326-May.... Case 427-May.... Case 528-May.... Case 629-May.... Case 730-May.... Case 831-May.... Case 901-Jun.... Case 1002-Jun.... Case 1103-Jun.... Case 1204-Jun.... Case 1305-Jun.... Case 1406-Jun.... Case 1507-Jun....

29 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?

30 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

31 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

32 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

33 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

34 Using simple packages for maps: Excel

35 Spot map: ornithosis cases by place of residence, East of England 2008, n=3

36 Spot map: ornithosis cases by place of residence, East of England 2008 (n=10)

37 Spot map: ornithosis cases by place of work, East of England 2008 (n=10)

38 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

39 Incidence map Invasive meningococal disease, East of England

40 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

41 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

42 Mapping an area exposure/determinant

43 Q fever: incidence and spot map

44 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

45 Graph exercise: reported reasons for not swimming at Lazareto (% responses)

46 Questions Message Graph type Style

47 First attempt: Select, Insert graph

48 Message: comparing proportions of responses

49 Type: Bar chart showing proportion by category

50 Style: reduce unnecessary ink

51 Dont forget the jellyfish


53 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

54 Step 1: Place transparency on the hardcopy of map to draw map with permanent marker Tips

55 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

56 Step 3: Remove the transparency and edit the map in the drawing software Tips

57 Your map is ready for use! Edit lines and fill, add title, legends and footnotes Tips

58 Fraction of HBV infections attributable to sharps injuries among health care workers, by region, 2000 North America Latin America Africa D Africa E W Europe Eastern Europe M. East South Asia S. E. Asia Western Pacific Australia Japan Gulf World Health Report, 2002 < 1% 1-9% 10-19% 20-29% 30-49% > 50% Former USSR Tips

59 Further functions of GIS Point in polygon Distance to vector (e.g. river, road) Raster – defining exposure areas –Satellite images Hotspot maps Interactive maps :

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