When you are looking at how something changes over time, the graph you need is the time series graph.

**What is a time series graph?**

Put simply, a time series graph is a graph that has** time along the bottom axis** and another **variable up the side.**

They can be used to find three things:

1) The** trend**. A trend shows if, over time, the variable you are looking at is getting bigger (positive, ascending) or smaller (negative, descending).

2) The** value **of the variable at a given time.

3)** When **the variable is increasing (or decreasing) at the greatest rate.

**Example: **

The data for birth rates in China from 1950 - 2010 is shown in this table.

Draw a time series graph for the data.

a) **Describe the trend** for the birth rate in China over time.

There is only one of two words you need here - increasing or decreasing. As the trend for the graph is **downwards,** we describe this as a **decreasing trend.**

b) Estimate the **birth rate **in 1972.

If we read up from 1972 on the graph and then read across, we get the answer of 5 children per family.

c) Between which two years did the birth rate **decrease the fastest?**

This is actually easier than it sounds. All we need to do is to look for where the line is the** steepest.**

This would be between 1970 and 1975.

Now, it's over to you.