Bad ways to sample 2 – Voluntary sampling

Voluntary sampling – Sample made up of volunteers.

In research many sampling techniques simply involve asking for volunteers.

Oh dear! These volunteers are a right bunch of nutters.

Problems with voluntary sampling

Voluntary sampling has a tendency to result in those with strong opinions being more willing to volunteer, thus creating a bias that overemphasises these views and underestimates those of people who do not care so much about the survey’s topic. The methods of how you obtain your volunteers can also impact the survey, for example advertising for survey volunteers in Stud and Tattoo magazine will result in a survey that is biased toward the opinion of this group and is unlikely to be representative of Muslim clerics.

Example

A radio show asks volunteers to call in with their opinions on gun control. Suggest why the opinions expressed may not be representative of the whole population.

Answer:

The radio station is only getting the opinions of those who listen to that station at that time of day and the demographics of these people may not match that of the general population. People with strong opinions on both sides are more likely to call in than those with more nuanced or moderate opinions who feel less passionately about the subject. This creates a bias of opinions which may not accurately express the overall opinion of the population.