Chapter 31
Presentation of
statistical data
31.1 Some statistical terminology
31.1.1 Discrete and continuous data
Data are obtained largely by two methods:
(a) By counting – for example, the number of stamps
sold by a post office in equal periods of time.
(b) By measurement – for example, the heights of a
group of people.
When data are obtained by counting and only whole
numbers are possible, the data are called discrete. Measured data can have any value within certain limits and
are called continuous.
Problem 1. Data are obtained on the topics given
below. State whether they are discrete or continuous
data.
(a) The number of days on which rain falls in a
month for each month of the year.
(b) The mileage travelled by each of a number of
salesmen.
(c) The time that each of a batch of similar
batteries lasts.
(d) The amount of money spent by each of several
families on food.
(a) The number of days on which rain falls in a given
month must be an integer value and is obtained by
counting the number of days. Hence, these data
are discrete.
(b) A salesman can travel any number of miles
(and parts of a mile) between certain limits and
these data are measured. Hence, the data are
continuous.
(c) The time that a battery lasts is measured and
can have any value between certain limits. Hence,
these data are continuous.
(d) The amount of money spent on food can only be
expressed correct to the nearest pence, the amount
being counted. Hence, these data are discrete.
Now try the following Practice Exercise
Practice Exercise 122 Discrete and
continuous data (answers on page 353)
In the following problems, state whether data relating to the topics given are discrete or continuous.
1. (a) The amount of petrol produced daily, for
each of 31 days, by a refinery.
(b) The amount of coal produced daily by
each of 15 miners.
(c) The number of bottles of milk delivered
daily by each of 20 milkmen.
(d) The size of 10 samples of rivets produced
by a machine.
2. (a) The number of people visiting an exhibition on each of 5 days.
(b) The time taken by each of 12 athletes to
run 100 metres.
DOI: 10.1016/B978-1-85617-697-2.00031-4
Presentation of
statistical data
31.1 Some statistical terminology
31.1.1 Discrete and continuous data
Data are obtained largely by two methods:
(a) By counting – for example, the number of stamps
sold by a post office in equal periods of time.
(b) By measurement – for example, the heights of a
group of people.
When data are obtained by counting and only whole
numbers are possible, the data are called discrete. Measured data can have any value within certain limits and
are called continuous.
Problem 1. Data are obtained on the topics given
below. State whether they are discrete or continuous
data.
(a) The number of days on which rain falls in a
month for each month of the year.
(b) The mileage travelled by each of a number of
salesmen.
(c) The time that each of a batch of similar
batteries lasts.
(d) The amount of money spent by each of several
families on food.
(a) The number of days on which rain falls in a given
month must be an integer value and is obtained by
counting the number of days. Hence, these data
are discrete.
(b) A salesman can travel any number of miles
(and parts of a mile) between certain limits and
these data are measured. Hence, the data are
continuous.
(c) The time that a battery lasts is measured and
can have any value between certain limits. Hence,
these data are continuous.
(d) The amount of money spent on food can only be
expressed correct to the nearest pence, the amount
being counted. Hence, these data are discrete.
Now try the following Practice Exercise
Practice Exercise 122 Discrete and
continuous data (answers on page 353)
In the following problems, state whether data relating to the topics given are discrete or continuous.
1. (a) The amount of petrol produced daily, for
each of 31 days, by a refinery.
(b) The amount of coal produced daily by
each of 15 miners.
(c) The number of bottles of milk delivered
daily by each of 20 milkmen.
(d) The size of 10 samples of rivets produced
by a machine.
2. (a) The number of people visiting an exhibition on each of 5 days.
(b) The time taken by each of 12 athletes to
run 100 metres.
DOI: 10.1016/B978-1-85617-697-2.00031-4