#### Revision Notes

##### What is a stem-and-leaf diagram?

A stemandleaf diagram is a simple but effective way of showing data.  It puts the data into order, puts it into classes (groups) and we can quickly see patterns.  As the data is in order it is also useful for finding the median and quartiles.

##### What do I need to know?

Stem-and-leaf diagrams are particularly useful for two-digit data but can be used for bigger numbers.  Two-digit data could be something like 26 but could also be 2.6. Due to this one of the essential things about a stem-and-leaf diagram is that it has a key.

You may also come across back-to-back stem-and-leaf diagrams which are used to compare two sets of data.

1. Stem-and-Leaf diagrams

The digits from the data is split into two – stems and leaves.  As in nature though, a stem can have more than one leaf. So the stems become our classes in our data.

eg The data value 26 would be split into a stem of 2 and a leaf of 6.

That will then mean the “2” becomes a class interval – ie the 20’s.

Any other values in the 20’s would join the same class – so a stem of 2 would have two leaves.

eg Draw a stem-and-leaf diagram for the following data

26  45  32  27  29  30  40  36  37

As the data is not in order draw a rough diagram first to get the data values into the correct format:

Key: 2|6 means 26

And add a key so we know what the data is showing.

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