# Effective graphs and maps

## Presentation on theme: "Effective graphs and maps"— Presentation transcript:

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)
Table –you really need to know exact time. Map/picture shows border of Haiti and Dominican Republic- deforestation in former. Graph conveys change over time.

Vaccine coverage in Yamoussoukro district, Ivory Coast, 1995
The exact % does not add anything and may be distracting 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 Message- think of linked text in paper. What graph best shows this –imagine seen as flashcard/subliminal.

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 Message is the only thing you would say about the graph if you had to describe it- or better still, what you wanted to show before you made the graph Framing the message

No clear message Symptom surveillance by region
Is there a message? How should this have been presented? Perhaps OK for a regular surveillance report

Two messages- too many? Weekly norovirus tests by result
Shows number of tests and % positive. Also juxtaposed bars

One message- varying proportion positive
Add graph on tests per week

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 80 60 40 Percentage 20 Ringed category is twice as wide as 50-99, in turn twice 0-19.9 > 300 Urinary Iodine Excretion levels (µg/L)

Epicurve: gastroenteritis at a music festival
One case one square

COLD/FLU CALLS: Daily ‘cold/flu’ calls as a proportion of total calls (7-day moving average) by region( ). 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
Whole is all positive samples

Alignment allows comparing proportions across groups
Cumulated bar chart for the breakdown of many totals in proportions Estimated and projected proportion of deaths due to non-communicable diseases, India, 100% 90% 80% Injuries 70% 60% Communicable Proportion (%) 50% diseases 40% Non communicable 30% diseases 20% 10% Alignment allows comparing proportions across groups 0% 1990 2000 2010 Year

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 This is where proportions don’t have to add to 100% across groups, or where there are too many groups for a pie or stacked bar to be clear 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 No logical order (categorical?) – no axis as would imply category between irregularity and lack of motivation Lack of facility Lack of money 0% 20% 40% 60% 80% 100% Analog information India FETP

Vertical bar chart: Gradient, but not quantified (No x axis)
Maternal education of mothers, vaccine coverage survey, Yamoussoukro, Ivory Cost, 1995 70 60 50 40 Frequency (%) 30 20 Logical order (ordinal) 10 None Prim Sec Sup Level of education Analog information EPIGEPS course of field epidemiology

Can use x axis as age is continuous
Prevalence of hypertension by age and sex, Aizawl, Mizoram, India, 2003 6 5 4 % 3 2 Can use x axis as age is continuous 1 3 - 3 9 4 - 4 9 5 - 5 9 6 - 6 9 7 + A g e g r o u p ( y e a r s ) Vertical bar chart: Quantified gradient (x Axis)

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

Putting it on the map: using maps in epidemiology
Lecture notes

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 Politics
Include if location is relevant to your key message Politics Some maps/borders/ comparisons are sensitive Avian influenza in Norfolk

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 Can use GPS or address- shows postcode location Case Onset
Other Geolocation 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 Can use GPS or address- shows postcode location

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 Now on to maps. Do not use tables to show geographical information: You would loose a lot of 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 Essentially a database linked to geolocation data 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) This is the basic spot map drawn in the field to spot cases. Field epi map

Using simple packages for maps: Excel
Map of cases of respiratory disease in a community hospital – any thoughts on mode of spread? In reality staff involved (not mapped!)

Spot map: ornithosis cases by place of residence, East of England 2008, n=3
First 3 cases were all hospitalised near there place of residence

Spot map: ornithosis cases by place of residence, East of England 2008 (n=10)
We asked cases where they worked, and they answered “poultry factory” – they did not know the address

Spot map: ornithosis cases by place of work, East of England 2008 (n=10)
Cases were transported to work via minibus, so they did not need to know the address

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 The incidence density map adjusts for population size. –where might this be helpful? It uses the count, divide and compare approach. Field epi map

Incidence map Invasive meningococal disease, East of England
This is 5 years’ data. You can spot the cities . Census data provided population

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
Also use surveillance data, eg. Prevalence. Test has to be on table data – meningitis risk higher in more deprived wards (local area)

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)

Questions Message Graph type Style

First attempt: Select, Insert graph
What’s wrong? Lots, but start with message. Should we put secular trend with comparison of proportions?

Message: comparing proportions of responses
But best to compare proportions using horizontal bar – and to sort by descending frequency

Type: Bar chart showing proportion by category
Categories are not ordered, so order by proportion

Style: reduce unnecessary ink

Don’t forget the jellyfish
There were two messages- don’t forget

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