S3.2.7 For the adult
Counting living things
How can anyone count the daisies in a whole field?
What this chapter teaches
A sample of a few frames, chosen at random, can estimate the number of plants in a field. The mean count in a frame, times the number of frames that fit, gives the estimate. Choosing the places by hand biases the result.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why do we count a sample and not the whole field?
- How do you work out the mean from the counts?
- Why did we draw numbers from a cup to place the frames?
After the chapter, the learner can
- Estimate the number of plants in a field using a square frame
- Explain why samples should be placed at random
What they copy into their notebook
Count plants in a few square frames put down at random. Find the mean count. Multiply by the number of frames that fit in the field. Random choice makes the sample fair.