Lesson video

Hello, my name's Miss Parnham, and in this lesson we're going to learn how to plot and interpret time series graphs.

In this example, we have some electricity bills.

Electricity bills, like all utility bills generally arrive every quarter this means quarter of a year and as a year is 12 months, that means every three months.

So we're now going to plot a time series graph and that means that we have a unit of time on the horizontal axis the other variable on the vertical axis and we're going to plot coordinates.

So our unit of time here is quarter because that means every three months and our axis will look something like this.

So on the first quarter we will plot 82 on the second 65 on the third 47 on the fourth 103 fifth is 70 pounds sixth 57 seventh we have 39 pounds and finally the eight quarter the bill was 89 pounds.

And the next thing we do is join up the successive points with straight lines.

These lines are simply there to show a trend.

Are the points falling? Are they rising? Are they generally staying the same? Are they fluctuating? All these things are when we are asked for a trend.

We never read off from the lines themselves, they're simply there to show a trend.

So why might the higher bills occur in the fourth and eighth quarters? Okay, just a little bit of real life common sense here there's probably and increased use of electricity in the colder months this must be the winter months due to cooking more food, we may have electric heating and lighting et cetera your does more using more power for various things.

Dexter is trying to reduce his energy consumption do you think he's achieved this? Well this is not about his consumption but it is about the cost of his energy and if we just look at the trend of the line it does seem to be generally falling obviously we get that fluctuation with the winter months but the trend is generally downwards so it does suggest he's using less.

Here's a question for you to try.

Pause the video to complete the task and then restart the video when you are finished.

Here are the answers.

We can have any unit of time on the horizontal axis and as you can see form this example it can be qualitative such as the days of the week.

Here's another question for you to try, pause the video to complete the task and the restart the video when you are finished.

Here are the answers.

This question shows that two sets of data can be plotted on the same axis we just have to make sure that we've got a key.

And now if you are plotting both sets of data, then plot the coordinates for one first and join with lines before then plotting the next set of coordinates and joining those with a line, otherwise, if you plot first and then draw your lines second you're going to get confused.

Here's a question for you try pause the video to complete the task and then restart the video when you are finished.

Here are the answers.

We must never ever read off data from the lines they're simply there to show a trend such as in this example a rise in temperature towards the middle of the day and then a fall in temperature as we move towards the evening.

Here's another question for you to try, pause the video to complete the task and then restart the video when you're finished.

Here are the answers.

You might not have word for word what is given as a sample answer here if you've said something like St Mary's records a lower average rainfall in the Winter or perhaps you've said Autumn or Spring that's equally valid but they do both have very similar rainfall in the summer even though we're talking about opposite ends of the United Kingdom.

That's all for this lesson, thank you for watching.