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Systematic Sampling

moving on to systematic sampling so

we've already looked at simple random

sampling we've looked at stratified

sampling cluster sampling if you haven't

seen those videos because you're

watching these out of order you can go

back and find those as well but let's

focus on systematic sampling I still

have my 30 people in my population and I

still like to have a sample size of 10

so my sample size is going to be 10 well

in order to get my 10 people I'm going

to use systematic sampling and it sounds

just like the title I'm going to create

a system in order to get my sample size

well what I'm going to end up doing is

I'm going to choose to start with the

second person in my population or if

these people are living on streets just

like we were looking at in cluster

sampling this was one street made this

one up here was Maple Street this one

was Main Street and this one was 1st

Street and I'm going to walk around the

neighborhood and interview them then I'm

going to choose to start with the second

house so I would interview this person

my plan or my system is going to be

start with the second house and I'm

going to interview every third house

after that or every third person that

lives in every third house so here we go

I start with my second house and then

I'm going to skip over to the next to

the every third house so I go 1 2 3 and

I interview this person and then go 1 2

3 and interview this person and they go

1 2 3 and interview this person and then

1 2 3 interview 1 2 3 interview 1 2 3

interview 1 2 3 interview 1 2 3

interview 1 2 3 interview this person

and now I should have my 1 2 3 4 5 6 7 8

9

in there is my sample size of 10 and

that is some systematic sampling if you

start somewhere in a new interview or

choose every third person after that or

every fourth person or every tenth

person it doesn't have you don't have to

start with the second one and go every

third I could have changed that up but

this concept is called systematic

sampling now I want you to notice

something about this particular sample

that I collected in this sample there

was only one blue person chosen no I

take that back there were only two

people chosen in that sample and there

was only two there were only two of the

red girls in that sample as well that

means that there were one two three four

five six of the black stickmen in that

particular sample so systematic sampling

is kind of nice and that's how you would

do it but at the same time systematic

sampling sometimes might lead to

something called bias and the bias in

this case would be that I'm getting more

of one type of stick man as opposed to

the other types

so sometimes systematic sampling is okay

but you have to be careful because in

this case it just so happened that there

were six of the black stick men only two

of the blue stick men and only two of

the red stick girls so systematic

sampling which you got to be careful