Loading subjects
Time Series · Part 1 of 2
6 exam-style questions with model answers, plus 8 quick multi-choice questions — every question on this part of the standard, grouped by the 2 pages of notes they come from.
Write a full answer before you reveal the model one. That comparison is where the learning happens.
Explain the difference between the trend, seasonal and irregular components of a time series.
A time series of monthly residential electricity demand for a New Zealand city shows a repeating annual pattern with peaks in June and July and troughs in January and February, and a slow upward trend across ten years. Describe these features and explain them in context.
A student is investigating quarterly sales for a New Zealand ice cream manufacturer over eight years. The seasonal swing between the Q1 peak and Q3 trough was about $180 000 in the first year and about $310 000 in the final year, while average quarterly sales roughly doubled over the period. The student fits an additive model. Evaluate this choice.
Explain why a 4-point moving average is used for quarterly data, and why it must be centred.
A student uses a 3-point moving average on quarterly data and finds the resulting trend still shows a regular zigzag. Explain what has gone wrong and what the consequence is.
A student's series of monthly hospital admissions shows a clear 12-month seasonal pattern, but also a sharp one-off spike in a single month caused by a major storm. She fits a centred 12-point moving average and notes the trend rises noticeably around that month. Discuss how she should handle this.