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 calleddiscrete. Mea-
sured data can have any value within certain limits and
are calledcontinuous.

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 byeach 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

countingthe number of days. Hence, these data

arediscrete.

(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 ismeasuredand

can have any value between certain limits. Hence,

these data arecontinuous.

(d) The amount of money spent on food can only be

expressed correct to the nearest pence, the amount

beingcounted. Hence, these data arediscrete.

Now try the following Practice Exercise

PracticeExercise 122 Discrete and

continuous data (answers on page 353)

In thefollowingproblems,statewhether data relat-

ing 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) Thesizeof10samplesofrivetsproduced
   by a machine.


2. (a) The number of people visiting an exhi-
   bition oneach 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