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6.2 Types of data

6.2 Types of data

When you carry out a statistical investigation, you need to know where to collect or "nd your data.

#ere are two types of data.
Primary data is data that you collect yourself. You can carry out an experiment, or you can do a survey
and ask people questions.
Secondary data is data that has already been collected by someone else. You can look, for example, in

books, newspapers, magazines or on the internet to "nd this data.

Worked example 6.2

a Shen is investigating the hypothesis: ‘Eight-year-old boys are taller than eight-year-old girls in the
village school.’ Should he use primary or secondary data?
b Tanesha is investigating the hypothesis: ‘In June, Madrid has more hours of sunshine than Milan does.’
Should she use primary or secondary data?

a Primary data Shen should carry out a survey in his village school. It wouldn’t take him long to
measure the heights of eight-year-old children and record the information.
b Secondary data Tanesha would have to get this information from weather records. She could use
the internet to look for weather records for Europe. She may also be able to get
this information from travel brochures.

) Exercise 6.2

1 Decide whether primary or secondary data should be used in each of these investigations.
Give a reason for each answer.
a Sasha is investigating whether children are taller now than they were 50 years ago.
b Anders is investigating whether boys prefer to eat an apple, an orange or a banana.
c Oditi is investigating whether there is more rainfall in India than there was 10 years ago.
d Ahmad is investigating the most popular brand of TV sold in his country.
e Alicia is investigating the average salary earned by government employees.
f Jake is investigating the favourite sport of 15-year-old children.
g Zalika is investigating the most popular size of shoes sold in her country.
h Xavier is investigating the number of visits people make to a dentist each year.
2 Hassan wants to find out the most popular colour of car that Work in pairs, or groups of three,

is sold in the USA. He finds data that shows the most popular to answer question 2.
colour of car that is sold in Europe is silver.

I can assume that silver is also the most
popular colour of car that is sold in the USA.

a Give a reason why Hassan could be right to make this assumption.
b Give a reason why Hassan could be wrong to make this assumption.

58 6 Planning and collecting data