AQA GCSE Statistics Time series: a complete overview of trends, moving averages and forecasting

What this module demands

Time series is about data collected over time. AQA tests whether you can read a time series graph, separate the trend from seasonal and random variation, smooth the data with moving averages, and forecast a future value with the seasonal effect added back. Calculation accuracy and a clear interpretation share the marks.

This guide walks through the three topics in specification order, then sets out the exam patterns AQA repeats. Each topic has a matching dot-point page with practice questions; this overview ties them together.

Time series graphs

The module opens with time series graphs: plotting data against time, identifying the trend, and distinguishing seasonal, cyclical and random variation. Seasonal variation, the regular repeating pattern, is the kind tested most.

Moving averages

Moving averages covers calculating a moving average, choosing the period to match the cycle (a $4$-point for quarterly, $12$-point for monthly data), centred moving averages, and plotting them to reveal the trend.

Trend lines and forecasting

Trend lines and forecasting covers drawing a trend line through the moving averages, calculating the mean seasonal effect (actual minus trend), and forecasting by extending the trend and adding the seasonal effect, while recognising that long-range forecasts are unreliable.

How this module is examined

A typical AQA profile for this module:

• Time series graphs. Identifying the trend and naming the type of variation.
• Moving averages. Calculating them with the correct period and plotting them.
• Trend lines. Drawing the line through the moving averages.
• Forecasting. Adding the mean seasonal effect to a future trend value and noting limitations.

Check your knowledge

A mix of recall and calculation questions covering this module. Attempt them under timed conditions, then check against the solutions.

1. Define the trend of a time series. (1 mark)
2. Quarterly sales peak every fourth quarter. Name this type of variation. (1 mark)
3. What period of moving average suits monthly data with a yearly cycle? (1 mark)
4. Find the first $4$-point moving average for $12, 18, 22, 8$. (2 marks)
5. Where should each moving average be plotted? (1 mark)
6. The seasonal effect is actual value minus which value? (1 mark)
7. The trend value next summer is $50$ and the mean seasonal effect is $+8$. Forecast the value. (2 marks)
8. Give one reason a long-range forecast may be unreliable. (1 mark)