الرحمن الله الرحمن بسم الله بسمالرحيمالرحيم

Dr. Laila Mohamed NofalProfessor of Biostatistics

High Institute of Public HealthUniversity of Alexandria

• Attract the reader’s attention

A graph or diagram, provides an easily understood

picture of the data. A suitable diagram is easier to

grasp and leaves a more permanent impression of the

main features of the data

• To compare two or more distributions.

Graphical presentation is the use of a graph to show the

distribution of data.

There are many varieties of graphs. The use of

a particular type depends on:

– Type of data (quantitative continuous or

discrete or qualitative)

– Type of table (simple or complex)

Graphical Presentation

One quantitative variable & Time.

Time may be years, months, weeks, days,

hours…)

No frequency distribution.

May be one or more quantitative variables

by time.

The Line Graph

• Example:

YearCrude Birth Rate Per 1000 Population

199750

199851

199953

200055

200152

The Line Graph

Figure (1) Crude birth rate of Country X 1997-2001

Figure (1) Crude birth rate of Country X 1997-2001

36.332.8

13.912.3 11.2 10.9

14.514.916.1

23.024.927.130.231.4

0

5

10

15

20

25

30

35

40

1970 1975 1980 1985 1990 1995 2000

Time (years)

CBR/

1000

popula

tion

Developed Countries Developing Countries

The Line Graph

• For quantitative continuous variables• S.F.D.T only

• Example:

Age in YearsFrequency

0 - 4

5 - 10

10 – 18

15 – 8

20 - 246

Total46

Y (Frequency or %)

X (Variable)

• Example:

Age in Years

Figure (2): Distribution of patients by age in Hospital X, 2011

• Quantitative continuous variable

• SFDT or Complex FDT

• SFDT

• Points are joined by straight line

• Complex FDT

• Points are joined by straight line

Distribution of a group of patients by ageDistribution of a group of patients by age

Age Age groupgroupFreq.Freq.

RelativeRelative

Freq.Freq.

(%)(%)

Mid-Point(abscissa)

20-20-6612.212.2(20+30)/2=25

30-30-181836.736.7(30+40)/2=35

40-40-111122.522.5(40+50)/2=45

50-50-111122.522.5(50+60)/2=55

60-6960-69336.16.1(60+70)/2=65

TotalTotal4949100.0%100.0%

01

02

0

0 25 35 45 55 65

Class Mid-Point

Fre

qu

en

cy

01

02

0

0 25 35 45 55 65

Class Mid-Point

Fre

qu

en

cy

Distribution of a group of patients by Distribution of a group of patients by ageage

• Example:

Age in YearsSexMid-point of interval

MalesFemales

20-3( 12%)2( 10%))20+30/(2=25

30-9( 36%)6( 30%)(30+40)/2=35

40- 7 (28%) 5( 25%))40+50/(2=45

50-4( 16%)3( 15%))50+60/(2=55

60-692( 8%)4( 20%)(60+70)/2=65

Total25 20

Figure (3): Distribution of patients by age and sex in Hospital X, 2012

0

5

10

15

20

25

30

35

40

25 35 45 55 65Age

%Males Females

• Quantitative continuous variable

• SFDT or Complex FDT

• Points are joined by a smooth curve

• The more the number of points (categories)

the more smooth will be the curve

0

5

10

15

20

25

30

35

0 30 40 50 60 70 .

Age (years)

%

Distribution of malaria cases by age

• Qualitative or quantitative discrete variables

• Simple or complex frequency table

• Simple frequency table

• Complex frequency table

Exampl

e

0

5

10

15

20

25

30

35

40

45

%

Single Married Divorced Widowed

Marital status

Distribution of a group of HIV cases by marital status

Bars should be of equal widths and inter bar spacing and differ only in

height

Exampl

e

0

10

20

30

40

50

%

Single Married Divorced Widowed

Marital statusDistribution of a group of HIV cases by marital

status and gender

Male

Female

The Pie Chart

• This type of graph can be used with all types of variables in simple frequency distribution tables.

1. The pie is divided into a number of sectors equal to the number of categories in the table so that each sector will represent one

category from the table.2. The starting line for sub-division of the circle is usually taken as 12

o’clock radius.3. The sub-division of the pie is usually in a clockwise direction.

4. The angle of the sector representing a particular category can be determined as follows:

angle = Frequency of each category X 360 Total frequency

The Pie Chart

• Angle for single = 20 x360 = 100⁰ 72• Angle for married = 30 x360 = 150⁰ 72• Angle for widowed= 10 x360 = 50⁰ 72• Angle for divorced= 20 x360 = 60⁰ 72• Total = 100+150+50+60= 360⁰

Marital StatusFrequency

Single20

Married30

Divorced10

Widowed12

Total72

The Pie Chart

Figure (4): Distribution of patients by marital status in Hospital X, in the year 2012

Pie ChartDistribution of patients according to their blood group and sex

Blood Blood GrouGrou

pp

SexSex

MaleMaleFemaleFemale

Freq.Freq.Rel. Rel.

Freq.Freq.

(%)(%)Freq.Freq.

Rel.Rel.

Freq.Freq.

(%)(%)

AA202027.827.8151525.925.9

BB303041.741.7181831.031.0

ABAB101013.913.9131322.422.4

OO121216.616.6121220.720.7

TotalTotal7272100.0100.05858100.0100.0

Pie Chart

Distribution of patients according to their blood group and sex

O16.6%

AB13.9%

B41.7%

A27.8%

O20.7%

AB22.4% B

31.0%

A25.9%

Male Female

GraphsGraphsGraphsGraphs

QuantitativeQuantitativeDataData

QuantitativeQuantitativeDataData

SFDTSFDT

Freq. PolygonFreq. Polygon

Freq. PolygonFreq. Polygon

HistogramHistogram

QualitativeQualitativeDataData

QualitativeQualitativeDataData

Complex Complex SFDTSFDT

Bar ChartBar Chart

Pie ChartPie ChartBar ChartBar Chart

ComplexComplex

ContinuousContinuousDiscreteDiscrete

Bar ChartBar Chart

DiscreteDiscreteContinuousContinuous

Bar ChartBar Chart