What’s trending? How to identify and describe trends

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What’s trending? How to identify and describe trends

Graphs and charts are some of the most efficient and effective ways of showing data. Therefore, being able to quickly and accurately extract useful information from a graph is a key skill for science subjects. So what should we be looking for when asked to ‘describe the trends’ shown on a graph?

Read the axes

You might have heard that you should always look at the axes first. This is very true. Read the axes labels and their units. What is this graph actually showing?

You’d be surprised how often people skim over the axes without reading them properly and end up interpreting the data in a completely different way. Is the y-axis showing death rate or disease prevalence? Is the x-axis showing time in minutes or volume of base added? Forgetting to read the axes can lead to vastly different (and incorrect) conclusions.

Identify the main comparisons

Are we comparing between different series on a line graph? Are we observing trends across the x-axis? Are we doing both?

If the questions says ‘trends’ (plural), then neglecting one or more apparent trends means that you are not answering the question correctly. So don’t rush into writing a response. Instead, take the time to look at all aspects of the graph to gain a full picture of the what the graph is telling you.

Be descriptive

If the questions says ‘describe’, then make sure you are descriptive. Is there a spike in disease incidence at a certain year? State the specific year. Does the slowly-increasing pH suddenly rise rapidly once a certain amount of base is added? State how much. Having a detailed description of trends can be important when you are asked to analyse relationships.

EXAMPLE

Let’s illustrate this with an example. The following graph shows canteen sales of a cold snack (ice pole) and a hot snack (party pie) at a primary school in Term 3. Obviously school canteen sales are not a part of HSC science, but it makes for a simple example.

Read the axes

The x-axis here indicates time, measured by the week of term. The y-axis is showing the absolute number of each product sold (not proportion of total sales).

Identify the main comparisons

One obvious comparison to make is to compare the sales of the two different products. In fact, based on the trends, their trends seem to oppose one another – when ice pole sales go up, party pie sales come down and vice versa.

We can also describe the trend in each series over time. Party pie sales are high at the start of term and generally trend to decrease, except for that spike at week 7. Ice pole sales start low and increase throughout the term, except for a dip at week 7.

Be descriptive

In addition to stating that ice pole sales mostly increase and party pie sales mostly decrease, we can note down exactly when the big changes happen. For example, week 5 is when we first start to see a marked rise in ice pole sales and fall in party pie sales. In week 7, the overall trend breaks and we see a sharp dip in ice pole sales and peak in party pie sales. Ice pole sales recover slightly in week 8 and continue to increase in week 9 and 10, with a slight dip in week 11, whereas party pie sales drop again in week 8 and stay low for the rest of the term.

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