Summary of Sampling Methods

We’ve now seen the five different types of sampling.

We’ve seen that volunteer and opportunity sampling are…

In volunteer sampling, the researcher posts an ad, and then people approach the researcher volunteering to be participants.

Whereas in opportunity sampling, the researcher directly approaches the participants, going for whoever is available and willing at the time.

They’re both quick and easy ways to sample! But, in both cases, the sample will not be very representative of the population. However, we know that…

However, we know that volunteer sampling is a bit easier than opportunity sampling.

And opportunity sampling is a bit more representative than volunteer sampling.

So, these two guys end up all the way down in this corner, like this

On the other hand, if we have a list of all the people in the population, we can do these other types of sampling:

Systematic sampling, where…

Systematic sampling is where the researcher picks every nth person from a list.

Or random sampling, where…

Random sampling is when a researcher chooses participants at random from a list of the entire population. This means that every member of the population has an equal chance of being a participant.

Now, in both cases, we’re picking from the whole population, so the samples are going to be far more representative than with volunteer and opportunity sampling.

But, with systematic sampling, if the list has a pattern that varies systematically, then the sample may not be totally representative. So the sample is less representative than with random sampling.

On the other hand…sometimes it’s more difficultto do random sampling, because…

Sometimes it’s more difficult to do random sampling, because you need to a way to randomise the list, either by putting names into a hat, or having a computer select random numbers. For instance, if you just have a hefty telephone book that’s not digitised, you’d need to assign a number to each entry which would take forever.

Whereas with systematic sampling, you could just pick every nth name, which is easier.

So, systematic sampling is a bit easier than random sampling.

Fifth and finally, we have stratified sampling, which is…

Stratified sampling is when researchers sample so that their sample has the same proportion of each subgroup as the total population.

Here we don’t necessarily need a list of the entire population, but we do need to know the proportion of each subgroup in the population.

With stratified sampling¸ the sample will represent all subgroups proportionately. So it’s the most representative type of sampling.

However, we need to know a lot about our population, making this more difficult than volunteer and opportunity sampling. And, because we need to divide our population into the important subgroups, there aremore steps involved than in random sampling…so it’s even more difficult. So it goes here.

And, there’s always a chance that we miss out an important subgroup by mistake, so, again, it’s still not totally representative.

For all these 3, we are sampling from the entire population, so our sample is going to be more representative.

However, they require knowledge of the whole population, like a list of everyone. So unfortunately, we often can’t use these types of sampling.

In psychology, we often just don’t have access to a list of the entire population that we’re studying.

For instance, Patty’s population is ‘depressed people’….there’s no way she can get a list of all depressed people!

Whereas other psychology studies might have a population like ‘children’…or ‘men’… or ‘Canadians’. 

For these studies, it’s not possible to have a list of the whole population, so researchers can’t use systematic, random or stratified sampling. 

So, most of the studies that you’ll see in psychology either use volunteer or opportunity sampling.

So, in summary, the five types of sampling are…

The five types of sampling are:

1.     Volunteer sampling

2.     Opportunity sampling

3.     Systematic sampling

4.     Random sampling

5.     Stratified sampling

Where…

Volunteer sampling leads to the least representative sample. As we go in this direction, samples get more representative, until we get to stratified sampling, which is the most representative type of sampling.

However, in terms of difficulty…

Stratified sampling is the most difficult type of sampling to conduct – you need to decide on the most important subgroups in the population, and make sure your sample has the same proportion as the population!

As we go down, the types of sampling get easier, until we get to volunteer sampling, which is the easiest type of sampling.

So, most of the studies that you’ll see in psychology use…

Most of the studies that you’ll see in psychology use volunteer and opportunity sampling. This is because they take much less time and effort than the other three types. 
And, we usually don’t have a list of the entire population that we’re studying!