Transcript Graphs and maps

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