median
don steward
mathematics teaching 10 ~ 16

## Saturday, 15 September 2012

### square sampling

Glyn Davies provided a resource like this in his helpful book (1993) 'Practical Data Handling Book B'

the task illustrates (intends to anyway...) how sampling a field of dandelions, ruled off into squares (or sampled using a quadrat) can be used to provide a reasonably accurate estimate of the size of a population

it is similar to the 'sampling circles' task

in three stages,
• students just pick a sample of 6 squares count the dandelions in these and multiply by 6 to obtain their estimate
• they then select a sample of 6 squares by chance using two dice (or one dice thrown twice) to generate the coordinates of the sample (it's fine to have the same square picked twice - sampling with replacement)
• they could also compare (in sub-groups) dice-selected samples of size: 3 (times 12), 9 ( times 4) and even 2 (times 18) to explore how accurate these are

it can be interesting to compare the class results for all of these

Glyn suggests drawing a number line and marking each student's result on it - to gain an appreciation of the data shape

the mean of the class results can be close to the actual population size