4. Number of children per woman
Count Frequency Relative Cumulative relative
frequency frequency
0 4 3.1 3.1
1 27 21.0 24.1
2 27 21.0 45.1
3 20 15.6 60.7
4 16 12.5 73.2
5 17 13.4 86.6
6 12 9.5 96.1
7 2 1.6 97.7
8 1 0.8 98.5
9 2 1.6 100
Total 128 100
5. Cumulative Frequency of Haemoglobin
Haemoglobin | Frequency Cumulative Cumulative
| frequency percentage
------------+----------------------------------------------
8- 8.9| 1 1 1.4
9- 9.9| 3 4 5.7
10-10.9| 14 18 25.7
11-11.9| 19 37 52.9
12-12.9| 14 51 72.9
13-13.9| 13 64 91.4
14-14.9| 5 69 98.6
15-15.9| 1 70 100.0
------------+---------------------------------------------
Total | 70
Cumulative
percentage of
women with HB
below 11 is
25.7%
6. Types of diagrams
• Histograms
• Cumulative frequency curve
• Scatter diagram
• Line diagram
7. Histogram
• a way of visualizing a frequency table
graphically to see
– most common values
– spread of data
• values of a variable or class intervals are
represented on the horizontal scale
• the vertical scale represents the frequency or
relative frequency at each value
• each bar centres at the mid point of the class
interval
8. Example: Distribution of number of
children per woman among 128 women
0 1 2 3 4 5 6 7 8 9
Number of children
0
5
10
15
20
25
30
Frequency
9. Example: Distribution of Haemoglobin among 70
women attending clinic
Hb Frequency Percentage
8 – 8.9 1 1.4
9.0 – 9.9 3 4.3
10.0 – 10.9 14 20.0
11.0 – 11.9 19 27.1
12.0 – 12.9 14 20.0
13.0 – 13.9 13 18.6
14.0 – 14.9 5 7.1
15.0 - 15.9 1 1.4
Total 70 100.0
0
2
4
6
8
10
12
14
16
18
20
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Haemoglobin
• Area of bars represent frequency
• Important to ensure every value accounted for
• Histogram gives a good representation of the distribution of the variable
10. Cumulative frequency curves
• the vertical axis displays cumulative
relative frequency
• the point is placed at the upper limit of the
interval
11. Cumulative Frequency of Haemoglobin
Median = 50%
Median HB = 12
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Haemoglobin
Not so easy to
see distribution
Easier to use for
different grouping
intervals
Avoid problems of
calculating heights
of bars for
equalising areas
12. Scatter diagram
• A scatter diagram is a graph used for examining
the relationship between two continuous
variables
• Diagram shows visually the shape and degree of
closeness of the relationship
• Each point on the diagram represents a pair of
values, one based on X-scale and the other
based on Y-scale
14. Line diagram
• These are often used to express the change
in some quantity over a period of time
0
50
100
150
200
250
300
350
400
450
500
1994 1995 1996 1997 1998 1999 2000 2001 2002
rate
per
100000
0-4
5--14
15-59
60+
Injury mortality rate in Hai District
15. Shapes of frequency distributions - 1
• 3 most common shapes
• All have high frequencies on the centre of the
distribution and low frequencies at the two
extremes
– called upper and lower tails of the distribution
16. Shapes of frequency distributions - 2
• Symmetrical (bell shaped)
• Asymmetrical or skewed
• Positively skewed (skewed to the right): upper tail
longer than lower tail
• Negatively skewed (skewed to the left): lower tail
longer than upper tail