An agricultural researcher is investigating dermatitis in sheep and wants to obtain a reliable indication of the prevalence. Sheep in the region are held on 213 properties of varying size, which have a range of soil and vegetation types. The distribution of the number of sheep per property is positively skewed (some big flocks, but most are smaller). All assessments are to be made on the home farms by the researcher or an assistant. Funds are available to assess skin conditions on about 360 sheep.

The assistant has suggested the following sampling method:

Randomly select 45 properties by means of computer-generated random numbers.

The number of sheep assessed on each selected property will be in proportion to the number of sheep on the property so that the total sample size is 360.

On each property, select every k th animal for assessment as it goes through the drenching chute, where k is chosen to give the correct sample size for the property.

For the suggested sampling method:

(a) Identify any elements of simple random sampling, convenience sampling, cluster sampling, systematic sampling, or stratified sampling.

(b) Briefly assess how well the method will meet the researcher's objective.

(c) Briefly describe the procedure's practical advantages and disadvantages compared with using strict simple random sampling.