EST. 2024 · LONDON·MMXXVI SPECIFICATION
AQA·Edexcel·OCR|Foundation + Higher
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Statistics & Probability · Foundation & Higher

Time series

A time series is data measured at regular intervals over time, shown on a line graph with time on the x-axis. Look for trends and seasonal patterns.

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Key facts to remember

  • 1Plot each data point and join with straight lines.
  • 2Time on the x-axis.
  • 3A trend is the overall direction — upward, downward, or stable.
  • 4Seasonal variation = regular repeating pattern.
  • 5A moving average smooths out seasonal variation to reveal the underlying trend.
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Worked examples

Example 1

A shop's quarterly ice-cream sales (thousands) are Q1:2, Q2:9, Q3:14, Q4:3, Q1:3, Q2:10, Q3:15, Q4:4. Describe the pattern.

Working

  1. Seasonal peaks in Q2/Q3, troughs in Q1/Q4.
  2. Same quarter year-on-year: each slightly higher in year 2.
  3. So: seasonal variation plus a rising overall trend.
AnswerSeasonal pattern peaking in summer (Q2/Q3), with a gentle upward trend year on year.
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Common mistakes

✗Confusing a trend with a seasonal peak.
✗Reading only one data point instead of the overall pattern.
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Exam tips

✓Describe both trend AND seasonal variation when asked.
✓Reference specific quarters/years from the graph when explaining.

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