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91580: Investigate time series data

Updated December 2016. This document has been updated in its entirety to address new issues that have arisen from moderation.

Students need to provide evidence of each component of the statistical enquiry cycle detailed in Explanatory Note 3 of the standard.

Selecting a variable to investigate

Sufficient time needs to be allocated for students to research the context and acquire appropriate contextual knowledge. At all levels of achievement the students need to select a variable to investigate and develop a question which is informed by this contextual knowledge. While students could investigate more than one time series or combine series, this is not a requirement of the standard.

Identifying features in the data

Features in the data need to include a quantitative description of the trend using the smoothed data.

It may be appropriate to describe the trend in sections if these are clearly identifiable in the display and are over a substantial period of time.

Features in the data also need to include a description of the seasonal pattern.

Using the model to make a forecast

Students need to make a forecast for at least one future time period in context. It is not sufficient to just produce a table of values. The accuracy of the forecast could be discussed by referring to the displays and by using the contextual knowledge gained from research.

Required quality of student response

For Merit, students need to justify all findings with reference to evidence from the displays and statistics, and link the purpose and findings to their research.

For Excellence, students need to integrate the statistical and contextual knowledge gained from their research throughout the response. They also need to reflect on the process, which could be shown by considering other relevant variables, evaluating the adequacy of the model or showing a deeper understanding of the models.

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