7: Evaluation

Reflecting on the PPDAC cycle, what could be improved next time?

At this point, the statistical inquiry cycle (PPDAC cycle) is complete, and you should have answered the investigative question.

Some things that might be worth considering on reflection are below. Not all of these will be applicable to the data set you investigate. It is not an exhaustive list.

Repeating for a new sample

If the ICI's only just overlap, or only just miss, then another sample might be useful. We know that the ICI will not always contain the population median, so we might be seeing a difference by chance.

Taking another sample might help confirm the inference being made - or raise more doubt.

Repeating with a bigger sample

If there is a small difference between the sample medians, but the ICI's overlap, then a bigger sample might help.

We could take a larger sample, which would reduce the size of the ICI's.

Remember that because of the square root in the formula

median ± 1.5 × IQR ÷ √n

the new sample will need to be quite a lot bigger to make much of a difference to size of the ICI's. Making the samples four times bigger would approximately halve the size of the ICI's.

Asking a new question

Is there another question that you could ask from the data set that is related to your investigative question? Is there another variable you would be interested in collecting if you were in charge of the data set? Returning to the Problem section of the PPDAC cycle could involve posing another investigative question.

You are not expected to conduct another statistical investigation.

Connecting to your research

In your problem you did some research into context - perhaps into what was already known about typical values of the numerical variable. Did you get the results you expected? How do your results related to the background information you gathered?

Investigating within a subgroup

Colouring the dot plot with a third variable might show a pattern that could be investigated further.

If two groups can be seen as separated, it might be worth investigating each one individually.

In this graph, it is clear that the male and female red-billed gulls have different weights. So we could investigate each group separately.

There is no PDF file for Worksheet 10.

For the final task on the Evaluation section, you need to complete a full investigation.

Choose any of the data sets (GULLS, NEWCARS or SCRABBLE), and write an investigative question. Work through the PPDAC cycle, including a final Evaluation.

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