# Systematic sampling help!

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Thread starter 7 months ago
#1
Is this still considered systematic sampling?

The population is 30 pets, for my sample I need 10 pets. My sample is 8cats and 2 dogs.

I create 1 list of all the cats, and pick every 2nd cat until I get to 8

I then create a separate list of all the dogs in the population and pick every 2nd dog until I get 2.

Is this still systematic sampling, or does it just have to be 1 list in the first place?

Thanks.
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7 months ago
#2
(Original post by smartiecookie)
Is this still considered systematic sampling?

The population is 30 pets, for my sample I need 10 pets. My sample is 8cats and 2 dogs.

I create 1 list of all the cats, and pick every 2nd cat until I get to 8

I then create a separate list of all the dogs in the population and pick every 2nd dog until I get 2.

Is this still systematic sampling, or does it just have to be 1 list in the first place?

Thanks.
Are you told that you must have 8 cats and 2 dogs? If so, why? Is it because this matches the proportions of cats and dogs in the population (i.e. there are 24 cats and 6 dogs)? If so, then I would say that your sample is stratified, but that it has been selected by systematic sampling.
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Thread starter 7 months ago
#3
(Original post by Pangol)
Are you told that you must have 8 cats and 2 dogs? If so, why? Is it because this matches the proportions of cats and dogs in the population (i.e. there are 24 cats and 6 dogs)? If so, then I would say that your sample is stratified, but that it has been selected by systematic sampling.
I meant to put 39 not 30 (sorry!). I wanted equal representation of cats and dogs, there are 33 cats and 6 dogs, so to get an equal proportion of each I did 25% from each group which resulted in 8 cats and 2 dogs.

Is it correct to use both stratfied and systematic?? I feel like I am only supposed to use 1 sampling method.

Do you think its more approriate to use stratified and random sampling instead of systematic? or it does not matter?
Last edited by smartiecookie; 7 months ago
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7 months ago
#4
(Original post by smartiecookie)
I meant to put 39 not 30 (sorry!). I wanted equal representation of cats and dogs, there are 33 cats and 6 dogs, so to get an equal proportion of each I did 25% from each group which resulted in 8 cats and 2 dogs.

Is it correct to use both stratfied and systematic?? I feel like I am only supposed to use 1 sampling method.

Do you think its more approriate to use stratified and random sampling instead of systematic? or it does not matter?
There are no formal rules as to what you are "supposed" to do. In the real world, you have to decide based on things like time and resources.

It seems quite sensible to want your sample to be representative of your population, so stratifying it is a good idea. If you do this, and you therefore know how many of each of cats and dogs you want, you then have to decide how you are going to select your samples from each group. You could do this in the way that you describe, using systematic sampling, but as your population is quite small, it wouldn't take a huge amount of time to make your dogs and cat samples truly random samples. Is there a reason why you would want to use systematic sampling? It's a good idea when you have large populations, as it saves a lot of time and effort, but in your case I would say it is worth the (small) extra time and effort to get a genuinely random sample.
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