Systematic Sampling

Summary

This video script introduces systematic sampling, a method where a sample is selected based on a fixed interval from a larger population. The example given involves choosing every third house in a neighborhood to interview, starting with the second house. While systematic sampling is straightforward and can be effective, it may also introduce bias if the population is not evenly distributed, as demonstrated by the disproportionate selection of 'stickmen' in the example. The script warns viewers to be cautious of this potential issue.

Takeaways

• 🔍 Systematic sampling is a method of selecting a sample from a population by establishing a system to select every nth element.
• 📝 The script discusses systematic sampling as an alternative to simple random, stratified, and cluster sampling methods.
• 📈 The example given involves a population of 30 individuals and a desired sample size of 10.
• 🏠 The method begins by choosing a starting point, in this case, the second house in a neighborhood.
• 🔢 After the initial selection, every third house (or person) is chosen to build the sample, ensuring a systematic approach.
• 🔄 The process involves skipping two houses and then interviewing the third, continuing this pattern to reach the sample size.
• 📊 Systematic sampling can be efficient and straightforward, but it may also introduce bias if the starting point or interval coincides with a pattern in the data.
• 🚨 The script warns that systematic sampling might lead to biased samples if not carefully planned, as demonstrated by the overrepresentation of one type of 'stickman' in the example.
• 📋 The example shows that only two blue and two red stickmen were selected, compared to six black stickmen, highlighting the potential for bias.
• 🔄 The script emphasizes the importance of being cautious with systematic sampling to avoid unintentional bias in the sample.
• 📚 Understanding the characteristics of the population and the potential patterns is crucial when using systematic sampling to ensure a representative sample.

Q & A

What is systematic sampling?

Systematic sampling is a method of selecting a sample from a population by establishing a system to choose members at regular intervals. It is a type of probability sampling that can be used when the population is large and a simple random sample is impractical.

How does systematic sampling differ from simple random sampling?

While simple random sampling involves selecting members from the population without any systematic pattern, systematic sampling involves choosing members at regular intervals, often starting from a randomly selected point.

What is the sample size in the given example of systematic sampling?

In the provided script, the sample size for the systematic sampling is 10.

How was the starting point chosen in the systematic sampling example?

In the example, the starting point was chosen to be the second person or the second house in the population.

What is the interval used in the systematic sampling example?

The interval used in the example is every third house or person after the starting point.

Why might systematic sampling lead to bias?

Systematic sampling can lead to bias if the starting point or the interval coincides with a pattern in the population, leading to an overrepresentation or underrepresentation of certain characteristics.

What was the potential bias observed in the systematic sampling example?

In the example, the potential bias was that there were more black stick men represented in the sample compared to blue and red stick people.

Can the starting point or interval in systematic sampling be changed?

Yes, the starting point and interval in systematic sampling can be changed to reduce the likelihood of bias and to better represent the population.

What is the importance of being cautious with systematic sampling?

Being cautious with systematic sampling is important to ensure that the sample is representative of the entire population and to avoid unintentional bias.

How can one ensure a more representative sample in systematic sampling?

To ensure a more representative sample, one can vary the starting point or interval, or use stratified systematic sampling where the population is divided into strata and samples are taken from each stratum.

What are some alternative sampling methods to systematic sampling?

Alternative sampling methods include simple random sampling, stratified sampling, cluster sampling, and convenience sampling, each with its own advantages and disadvantages depending on the research context.

Outlines

00:00

📊 Introduction to Systematic Sampling

The script introduces systematic sampling as a method of selecting a sample from a population. It begins by referencing other sampling techniques such as simple random, stratified, and cluster sampling, suggesting that viewers should watch those videos for a comprehensive understanding. The focus then shifts to systematic sampling, where the narrator aims to select a sample of 10 from a population of 30 individuals. The process involves creating a system to select every third individual starting from the second person in the population, which could be likened to selecting every third house in a neighborhood for an interview. This method is straightforward but requires careful consideration to avoid potential bias.

Keywords

💡Systematic Sampling

Systematic sampling is a probability sampling method where elements are selected from an ordered population at regular intervals. In the video, the concept is illustrated by starting with the second house and then selecting every third house thereafter to form a sample of 10. This method ensures a structured approach to sampling, which is crucial for maintaining consistency and reducing bias in the selection process.

💡Population

In the context of the video, the population refers to the total group of individuals or objects from which a sample is drawn. The video mentions a population of 30 people, which is the group from which the systematic sample of 10 is selected. The population is the basis for any sampling method, as it represents the entire group that is being studied.

💡Sample Size

Sample size denotes the number of individuals or observations included in a sample. The video specifies a sample size of 10, which means that out of the 30 people in the population, only 10 will be selected for the study. The sample size is an important factor in determining the representativeness and statistical power of the sample.

💡Bias

Bias in sampling refers to a systematic deviation from the intended distribution of the population in the sample, leading to inaccurate or distorted results. The video script points out that systematic sampling can sometimes introduce bias, as seen when the sample ended up with a disproportionate number of black stick men compared to blue and red stick figures, which could skew the findings.

💡Randomness

Randomness is the quality of being unpredictable or subject to chance, which is an essential aspect of many sampling methods to ensure that every member of the population has an equal chance of being selected. Although systematic sampling is not random in the traditional sense, the video mentions starting with the second person as a way to introduce an element of randomness into the selection process.

💡Stratified Sampling

Stratified sampling is a method where the population is divided into subgroups or 'strata' that share similar characteristics, and samples are then taken from each stratum. The video script mentions this method in the context of having previously discussed different sampling techniques, indicating it as an alternative approach to systematic sampling.

💡Cluster Sampling

Cluster sampling involves dividing the population into groups or 'clusters' and then randomly selecting some of these clusters for the study. The video uses the analogy of streets as clusters, where the houses (or people living in them) represent the population elements, to explain how cluster sampling works in comparison to systematic sampling.

💡Simple Random Sampling

Simple random sampling is the most basic form of probability sampling where every member of the population has an equal chance of being selected. The video script refers to this method as one that has been discussed previously, positioning it as a contrast to the systematic sampling technique being explained.

💡Representativeness

Representativeness in sampling refers to the extent to which a sample accurately reflects the characteristics of the population from which it is drawn. The video script implies that systematic sampling can affect representativeness, as the sample collected may not be a true reflection of the population's composition due to potential bias.

💡Sampling Interval

The sampling interval in systematic sampling is the regular space between the selected elements in the sample. In the video, the interval is established as every third house or person, which is a key component of the systematic sampling method described.

💡Stick Men

In the video script, 'stick men' are used as a metaphorical representation of individuals in the population, differentiated by colors to illustrate the concept of bias in systematic sampling. The term 'stick men' helps to visualize the sampling process and the potential for disproportionate representation of certain groups within the sample.

Highlights

Introduction to systematic sampling as a method following simple random, stratified, and cluster sampling.

Systematic sampling is chosen for a sample size of 10 from a population of 30.

The decision to start with the second person in the population for systematic sampling.

The systematic approach of interviewing every third house or person in the sequence.

Illustration of the systematic sampling process using a neighborhood example.

Starting with the second house and then moving to every third house for interviews.

Completion of the sample size of 10 using the systematic sampling method.

Discussion on the potential bias in systematic sampling due to the selection pattern.

Observation that the sample collected included an unequal number of different types of 'stickmen'.

Explanation of how systematic sampling can lead to bias by over-representing one group.

The importance of being cautious with systematic sampling to avoid unintentional bias.

The acknowledgment that systematic sampling is a valid method but requires careful application.

The concept that systematic sampling does not always have to start with the second item or person.

The flexibility in systematic sampling to choose different intervals for selection.

The practical demonstration of systematic sampling with a clear example of its process.

The conclusion that systematic sampling needs to be executed with awareness of potential biases.

Transcripts

moving on to systematic sampling so

we've already looked at simple random

sampling we've looked that 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 sides 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 M this one

up here was Maple Street this one was

Maine Street and this one was first

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

um 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

third to to the every third house so I

go one two three and I interview this

person and then go one two three and

interview this person and then go one

two three and interview this person and

then one two three interview one two

three interview one two three interview

one two three interview one two three

interview one two three interview this

person and now I should have my 1 two

three four five six seven 8 nine 10

there is my sample size of 10 and that

is simp systematic sampling if you start

somewhere and then you interview or

choose every third person after that or

every fourth person or every 10th person

it doesn't 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 nope I take that

back there were only two people chosen

in that sample and there was

only there were only two of the red

girls in that sample as well that means

that there there were one two three four

five six of the black stick men 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

Stickman as opposed to the other type 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 but you got to be careful