What is Data?
Data is a collection of facts, such as numbers, words, measurements, observations
or even just descriptions of things.
Qualitative vs Quantitative
Data can be qualitative or quantitative.

Qualitative data is descriptive information (it describes something)

Quantitative data, is numerical information (numbers).
And Quantitative data can also be Discrete or Continuous :

Discrete data can only take certain values (like whole numbers)

Continuous data can take any value (within a range)
Put simply: Discrete data is counted, Continuous data is measured

(Discrete)
Collecting
Data can be collected in many ways. The simplest way is direct observation.
Example: you want to find how many cars pass by a certain point on a road in a
10-minute interval.
So: stand at that point on the road, and count the cars that pass by in that
interval.
We collect data by doing a Survey .
Census or Sample
A Census is when we collect data for every member of the group (the whole
"population").
A Sample is when we collect data just for selected members of the group.
Example: there are 120 people in your local football club.
You can ask everyone (all 120) what their age is. That is a census.
Or you could just choose the people that are there this afternoon. That is a
sample.
A census is accurate, but hard to do. A sample is not as accurate, but may be
good enough, and is a lot easier.
Language
Data or Datum?
The singular form is "datum", so we say "that datum is very high".
"Data" is the plural so we say "the data are available", but it is also
a collection of facts, so "the data is available" is fine too.
Bar Graphs
A Bar Graph (also called Bar Chart) is a graphical display of data using bars of
different heights.
Imagine you just did a survey of your friends to find which kind of movie they
liked best:
Table: Favorite Type of Movie
Comedy
Action
Romance
Drama
SciFi
4
5
6
1
4
We can show that on a bar graph like this:
It is a really good way to show relative sizes: we can see which types of movie are
most liked, and which are least liked, at a glance.
We can use bar graphs to show the relative sizes of many things, such as what
type of car people have, how many customers a shop has on different days and so
on.
Example: Most Popular Fruit
A survey of 145 people revealed their favorite fruit:
Fruit: Apple Orange Banana Kiwifruit Blueberry Grapes
People:
35
30
10
25
40
5
And here is the bar graph:
For that group of people Blueberries are most popular and Grapes are the least
popular.
Example: Student Grades
In a recent test, this many students got the following grades:
Grade:
A
B
C
D
Students:
4
12
10
2
And here is the bar graph:
You can create graphs like that using our Data Graphs (Bar, Line and Pie) page.
Histograms vs Bar Graphs
Bar Graphs are good when your data is in categories (such as "Comedy",
"Drama", etc).
But when you have continuous data (such as a person's height) then use
a Histogram .
It is best to leave gaps between the bars of a Bar Graph, so it doesn't look like a
Histogram.
Pie Chart
Pie Chart - A special chart that uses "pie slices" to show relative sizes of
data.
Imagine you just did a survey of your friends to find which kind of movie they
liked best.
Here are the results:
Table: Favorite Type of Movie
Comedy
Action
Romance
Drama
SciFi
4
5
6
1
4
You could show that by this pie chart:
It is a really good way to show relative sizes: it is easy to see which movie types
are most liked, and which are least liked, at a glance.
You can create graphs like that using our Data Graphs (Bar, Line and Pie) page.
Or you can make them yourself ...
How to Make Them Yourself
First, put your data into a table (like above), then add up all the values to get a
total:
Comedy
Action
Romance
Drama
SciFi
TOTAL
4
5
6
1
4
20
Next, divide each value by the total and multiply by 100 to get a percent:
Comedy
Action
Romance
Drama
SciFi
TOTAL
4
5
6
1
4
20
4/20 = 20% 5/20 = 25% 6/20 = 30% 1/20 = 5% 4/20 = 20%
100%
Now you need to figure out how many degrees for each "pie slice" (correctly called
a sector ).
A Full Circle has 360 degrees, so we do this calculation:
Comedy
Action
Romance
Drama
SciFi
TOTAL
4
5
6
1
4
20
1/20 = 5%
4/20 =20%
100%
4/20 =20% 5/20 =25% 6/20 =30%
4/20 × 360° 5/20 × 360° 6/20 × 360° 1/20 × 360° 4/20 × 360°
= 72°
= 90°
= 108°
= 18°
= 72°
360°
Now you are ready to start drawing!
Draw a circle.
Then use your protractor to measure the degrees of
each sector.
Here I show the first sector ...
... you can do the rest!
Line Graphs
Line Graph - A graph that shows information that is connected in some
way (such as change over time)
You are learning facts about dogs, and each day you do a short test to see how
good you are. These are the results:
Table: Facts I got Correct
Day 1
Day 2
Day 3
Day 4
3
4
12
15
And here is the same data as a Line Graph: