Effective graphs The visual display of quantitative information FETP India.
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Transcript of Effective graphs The visual display of quantitative information FETP India.
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 amDigital and analogical information
Cases of Monkeypox by month of onset, Katako-Kombe, Zaire,
1996-1997Primary cases Secondary cases
Feb-96 2 0Mar-96 0 3Apr-96 2 2May-96 5 6Jun-96 0 5Jul-96 4 9Aug-96 3 23Sep-96 1 5Oct-96 1 2Nov-96 3 1Dec-96 0 0Jan-97 2 0Feb-97 1 9Total 24 65
Example: Digital display of informationWHO-CDC
Digital and analogical information
Nu
mb
er
of c
ase
s
Month of onset
Cases of monkeypox by month of onset, Katako-Kombe, Zaire,
1996-1997
0
5
10
15
20
25
30
Feb Mar Apr May Jun1996
Jul Aug Sep Oct Nov Dec Jan1997
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
33
42
52
75
79
0 20 40 60 80 100
Y. fever
Measles
DTP3
DTP1
BCG
Coverage (%)
EPIGEPS course of field epidemiologyDigital 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,
1996-2002
0
2
4
6
8
10
12
14
16
1996 1997 1998 1999 2000 2001 20002
Years
Pro
po
rtio
n (
%)
Is the graph useful?
Sources of hepatitis A virus infection among case-patients reporting at least one exposure, USA, 1983-1995
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
Year
Pro
port
ion
of c
ases
Day care related
Contact with a case
Common source outbreakForeign travel
Injecting drug useMen who have sex with men
Information on irrelevant risk
factors
Dilution of the information on injection drug
useCDC
Proportion of hepatitis A cases-patients reporting injection drug use*,
USA, 1983-1995
0%
2%
4%
6%
8%
10%
12%
14%
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
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
CDCFraming 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 incidenceBam and Oubritenga, Burkina, Faso,
1989-1992
0
20
40
60
80
100
1989 1990 1991 1992
Years of the project
Inci
denc
e p.
100
00
Bam
Oubritenga
OCCGE
1989 1990 1991 1992
BamOubritenga
020406080
100
Incidence p. 10000
Years of the project
Bam Oubritenga
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
0
20
40
60
80
0-19.9 20-49.9 50-99.9 100-300 > 300
Urinary Iodine Excretion levels (µg/L)
Pe
rce
nta
ge
HistogramUrinary iodine excretion
status, 24 N Parganas, West Bengal, India, 2004
Cases of acute diarrhea by date of onset, Parbatia,
Orissa, India (n= 41)
0
2
4
6
8
10
12
14
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
Date of onsetNovember 2003
Num
ber
of c
ases
Analog informationIndia FETP
Epidemic curve
Malaria in Kurseong block, Darjeeling District, West Bengal, India, 2000-2004
0
5
10
15
20
25
30
35
40
45
Janu
ary
Feb
ruar
y
Mar
chA
pril
May
June
July
Aug
ust
Sep
tem
ber
Oct
ober
Nov
embe
r
Dec
embe
rJa
nuar
yF
ebru
ary
Mar
chA
pril
May
June
July
Aug
ust
Sep
tem
ber
Oct
ober
Nov
embe
r
Dec
embe
r
Janu
ary
Feb
ruar
yM
arch
Apr
ilM
ayJu
neJu
lyA
ugus
t
Sep
tem
ber
Oct
ober
Nov
embe
r
Dec
embe
rJa
nuar
y
Feb
ruar
yM
arch
Apr
ilM
ay
June
July
Aug
ust
Sep
tem
ber
Oct
ober
Nov
embe
rD
ecem
ber
Janu
ary
Feb
ruar
yM
arch
Apr
il
May
June
July
Aug
ust
Sep
tem
ber
Oct
ober
Nov
embe
rD
ecem
ber
2000 2001 2002 2003 2004
Months
Inci
denc
e of
mal
aria
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
Road10%
Fall32%
Bites16%
Burns7%
Minor injuries35%
Types of unintentional injuries, Tiruchirappalli, Tamil Nadu,
India, 2003
Incidence: 9.6 per 100 person-month
(95% C.I. 8-11
Pie chart for the breakdown of a total in proportions
Estimated and projected proportion of deaths due to non-communicable diseases,
India, 1990-2010
0%10%20%30%40%50%60%70%80%90%100%
1990 2000 2010
Year
Proportion (%)
Injuries
CommunicablediseasesNon communicablediseases
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
Fre
qu
ency
(%
)
0
10
20
30
40
50
60
70
None Prim Sec Sup
Maternal education of mothers, vaccine coverage survey,
Yamoussoukro, Ivory Cost, 1995
Analog informationEPIGEPS 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)
0
10
20
30
40
50
60
30-39 40-49 50-59 60-69 70 +
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
Nu
mb
er
of c
ase
s
Month of onset
Cases of monkeypox by month of onset, Katako-Kombe, Zaire,
1996-1997
0
5
10
15
20
25
Feb Mar Apr May Jun1996
Jul Aug Sep Oct Nov Dec Jan1997
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 informationCDC-WHO
Nu
mb
er
of c
ase
s
Month of onset
Cases of monkeypox by month of onset, Katako-Kombe, Zaire,
1996-1997
0
5
10
15
20
25
30
Feb Mar Apr May Jun1996
Jul Aug Sep Oct Nov Dec Jan1997
Feb
Secondary cases
Primary cases
Cumulated bars respect the
representation of the dynamic of the outbreak and illustrate the break down
of cases
Analog informationCDC-WHO
Deciding the type of graph that is needed
Yes!Vertical bar chart
(no intervals)
No!Line graph
(Times series)
Yes!Epidemic curve?
Yes!Histogramme
Yes!Pie chart
No!Juxtapozed bars
cumulating to 100%
Yes!Only one total?
Quantified gradientx axis
No quantified gradientno x axis
Yes!Vertical bars ranked
by categories in logical order
No!Horizontal bars ranked
by magnitude of proportions
Yes!Logical order inthe categories?
No!Is is reporting proportions
in various categories?
No!Break down of 1 or
more totals in proportions?
No!Frequency distribution?
Event followed over time?
Take home messages
• Know when you want to use a graph • Know what your graph will say• Tailor your graph to your message