Collecting Data and Making Tally Charts

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What this lesson covers

  • Data is information we collect about the world.
  • A variable is the thing we find out about, like favourite pet.
  • A categorical variable sorts answers into groups called categories.
  • We can count how many answers are in each category.
Key idea

What is data?

  • Data is information we collect about the world.
  • We collect data to answer a question.
  • Our question: What are the favourite pets of students in our class?
Key idea

Variables and categories

  • The variable is the thing we find out about. Here it is favourite pet.
  • The answers sort into groups, called categories: dog, cat, fish.
  • A variable that sorts answers into groups is a categorical variable.
VariableCategories
favourite petdog, cat, fish, other
colour of shoesblack, white, blue, other
how we get to schoolwalk, car, bus, bike
Key idea

Ask a good question

  • Give a few choices, so the answers fit into a small number of categories.
  • Which fruit do you like best: apple, banana or kiwifruit?
  • Ask everyone the same question, and count each answer once.
Worked example

Sorting answers, and other

  • Room 2 gave these answers: dog, cat, dog, fish, lizard, cat, dog, axolotl.
  • Only one person said lizard and one said axolotl.
  • Put rare answers together in a category called other.
CategoryAnswers
dog3
cat2
fish1
other2 (lizard, axolotl)
Key idea

Try it: sort the answers

Key idea

Tally marks

  • Make one mark for each answer.
  • Draw 4 marks side by side. The 5th mark goes across the 4, like a gate.
  • Then count the gates in 5s and add the marks left over.
Worked example

Count the tally chart

  • Room 4 answered the pet question. Here are their tallies.
15 students altogether
PetTallyCount
dogone gate and 1 mark6
cat4 marks4
fish2 marks2
other3 marks3
Key idea

Try it: turn counts into a graph

Common mistakes

  • Making a new category for every rare answer.
    Put rare answers like lizard or axolotl together in other.
  • Drawing the 5th tally mark next to the other four.
    The 5th mark goes across the four. Then you can count in fives.
  • Asking "What do you like?" with no choices.
    Give a few choices, so the answers fit into a small number of categories.

Your turn

1

In the question "What is your favourite fruit?", what is the variable?

2

A tally shows one gate and 3 more marks. How many is that?

3

Only 1 student says guinea pig for favourite pet. Which category can it go in?

4

Dog has 6 tallies and cat has 4. How many more students chose dog?

5

Is colour of your bag a categorical variable?

Show answer

1. favourite fruit 2. 8 3. other 4. 2 5. yes, the colours sort into groups

Summary

What to take away

  • Data is information collected to answer a question.
  • A categorical variable sorts answers into categories.
  • Rare answers can go in other.
  • Tally in gates of 5, then count.
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