The diagram (right) shows the basic parts of the modern plough: 1  beam. 2  hitch (Brit: hake) 3  vertical regulator. 4  coulter (knife coulter pictured, but disk coulter common) 5  chisel (foreshare) 6  share (mainshare) 7  mouldboard.
Non-probability sampling is a type of sampling technique whereby all the units of a population do not have an equal chance of being selected in the sample.
Two of the main types of non-probability sampling methods are voluntary samples and convenience samples. 1  Voluntary sample. 2  A voluntary sample is made up of people who self-select into the survey. 3  Often, these folks have a strong interest in the main topic of the survey.