iii. Unusual Points

The next step involves a little bit of mathematical calculations. To work out if a point is an outlier we tend to use the rule of thumb that the residual is more than 10% of the overall spread. NZGrapher automatically draws these in as light grey lines for you in the residuals section. To easily identify points if you tick the ‘Point Labels’ button it puts the id of the row next to each point.

To calculate this we use the following calculation:

If any of the residuals are either larger or smaller than this value we need to comment on them and what might be causing them. You could also be thinking about how big the variation is of the residuals is as a component of the overall variation.

For each of the graphs calculate if there are any outliers and comment on any unusual features.

The first two have been done for you.

Remember:

To get higher grades, you need to contextualise your findings.

Once you have performed your analysis, you will need to relate your findings back to the problem you are investigating.

i.e What do the results mean for YOUR PROBLEM.

1. Sea Ice

Absolute Highest Value: 14

Absolute Lowest Value: 3

2. Births and Deaths

Absolute Highest Value: 8700

Absolute Lowest Value: 6700

Looking at the residuals graph due to the inconsistency of the data there are a large number of residuals between 2007 and 2010 that are outside the acceptable range. This is during the financial boom so it may be due to people being more willing to have children and therefore not worrying about the timing so much, therefore the normal patterns do not happen.

3. Penguins

4. Visitors

5. Imports

6. Forests

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