Year 4StatisticsInterpretation of dataYear 4 Maths

Reading a dot plot properly

What this lesson covers

  • Interpreting a data visualisation includes describing its variables and their units, the context for the data, and the visualisation’s key features: its shape (e.g. the number of peaks) its middle group(s) (where the middle of the data lies) its spread (how spread the data is from the minimum (lowest) value to the maximum (highest) value).
Key idea

Every dot is a person

  • Eleven children were asked how many pets they have.
  • Each dot is one child.
  • Remember that and the rest gets much easier.
Every dot is a person
Key idea

Two things are being counted

  • How tall a stack is counts PEOPLE.
  • Where a stack sits counts PETS.
  • Two different things, in one picture.
up the way: people. Along the way: pets
this bit of the picturecounts
one dotone person
how tall a stack ishow many people
where a stack sitshow many pets
Worked example

Question one: how many pets?

  • "How many pets does the person with the most pets have?"
  • Find the dot furthest to the right.
  • It sits above 5. So the answer is 5 pets.
Question one: how many pets?
Worked example

Question two: which is commonest?

  • "What is the commonest number of pets?"
  • Find the TALLEST stack. That is the one at 2.
  • The answer is 2 pets. Not 4.
Question two: which is commonest?
Key idea

Why the answer is not 4

  • The tallest stack has 4 dots in it.
  • But 4 is how many PEOPLE, not how many pets.
  • The question asked about pets. So read underneath.
the commonest mistake in the whole topic
if you answeryou have saidbut the question asked about
44 peoplepets
22 petspets (correct)
Key idea

So ask yourself first

  • Before you answer: is this about pets, or about people?
  • Pets: read along the bottom.
  • People: count the dots.
name what you are counting, then answer
questionaboutso
how many pets does the person with the most have?petsread along the bottom
what is the commonest number of pets?petsfind the tallest stack, read below it
how many people have 2 pets?peoplecount the dots in that stack
Key idea

Describing the shape

  • Step back and look at the outline.
  • Is there one lump, or two, or none?
  • This one has a single peak, at 2 pets.
Describing the shape
Key idea

Where it starts and where it stops

  • The lowest answer was 0 pets. The highest was 5.
  • So the answers spread from 0 to 5.
  • That is 5 apart, end to end.
Where it starts and where it stops
Key idea

Say what it is actually about

  • Never just say "the answer is 2".
  • Say "2 pets, that is the commonest in this class".
  • A number with no context has not told anyone anything.
the units and the group, every time
not thisthis
"5""the most any child had was 5 pets"
"4""4 children have 2 pets each"
"0 to 5""answers ranged from 0 to 5 pets"
Your turn

Your turn

  • How many children have exactly 3 pets?
  • What is the fewest pets anybody has?
  • How many children were asked altogether?
Your turn
Show answer

2 children: count the dots in the stack above 3, so this one is about PEOPLE. 0 pets: the leftmost dot, so this one is about PETS. 11 children: count every dot on the whole plot. Make them say "people" or "pets" before each answer; getting the right number for the wrong reason is the thing that catches up with them later.

Summary

Reading the picture

  • Every dot is one person.
  • Ask whether the question is about people or about the thing.
  • Then answer with the units, not just a number.
pause here
ideawhat to remember
one dotone person
stack heighthow many people
stack positionhow many pets
"commonest"tallest stack, read underneath it
shapehow many lumps, and where
spreadlowest to highest
every answersay the units and who was asked

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