Guide to population vs. sample in research

Gathering data for research projects can seem overwhelming and complex. There are many types of data available, and understanding the differences between them is critical to conducting effective research. In this guide, we'll be focusing on two main types: population and sample data. 

Population data consists of information collected from every individual in a particular population. Meanwhile, sample data consists of information taken from a subset—or sample—of the population.

In this guide, we’ll discuss the differences between population and sample data, the advantages and disadvantages of each, how to collect data from a sample and a population, and common sampling techniques. By the end, you'll have a better understanding of the differences between population and sample data and when to use them.

Population data is the total number of measurements taken from every individual within a group. For example, if you were measuring the heights of all humans on Earth, you’d include all 7 billion people in your population data set. 

When analyzing population data, researchers use statistics such as the population mean, median, and standard deviation. 

Types of populations

Finite population

A finite population is a population in which all the members are known and can be counted. Examples of this type of population include all the employees of a company, all the students in a school, or the entire population of a city. When working with a finite population, you can calculate the exact population mean, median, and standard deviation.

Infinite population

An infinite population is a population that is too large to be measured or counted. This could be the entire human population on Earth or the number of stars in the sky. Because it’s impossible to measure or count these populations, it isn’t possible to calculate their exact mean, median, and standard deviation.

Closed population

A closed population is one in which you allow no new members to join. An example of a closed population would be a country's citizens over the age of 18 who have been living there for more than 10 years. As no new members can join, the population remains constant and can easily be measured and analyzed.

Open population

An open population is one in which new members can join. For example, all people living in a certain city are considered an open population because new members can move into the city and become part of the population. This type of population is constantly changing, so it isn’t possible to measure and analyze its exact characteristics.

Advantages of population data

Representative

It offers a complete representation of all elements in the population, which can increase the generalizability of findings.

High quality

Population data is usually very accurate and detailed because standardized data collection methods and quality control measures are in place to provide data from every element in the population.

Large sample size

The sample size is large, which can increase the statistical power of a study and help detect small but meaningful differences. 

Can address rare events

You can use population data to study rare events or diseases that wouldn’t be feasible to study through other methods.

Allows for subgroup analysis

You can use population data to examine subgroups of the population, which can help identify disparities and inform interventions. 

Disadvantages of population data

Time and cost constraints

Collecting data from a large population is expensive and time-consuming, especially when it comes to data cleaning and preparation before using it for analysis.

Limited access

Depending on the source of population data, it can be difficult to get access to the population or convince people to participate, especially when there are privacy concerns or restrictions on the use of data.

Limited variables

Population data may have limited variables or lack information on important factors, which may not allow one to answer a particular research question if the data wasn’t originally collected for that purpose.

Difficult to analyze

Population data can be large, complex, and contain a wide variety of data or even missing data which demands advanced analytical skills and high computational requirements. 

Outdated information

Population data may become outdated, especially if it was collected some time ago, which can limit its relevance to current research questions. 

Sampling is the process of selecting individuals from a larger population and is used to generate representative information about the population of interest. There are two forms of sampling: non-probability. 

Probability sampling is from a randomly selected small subset and provides statistical inferences about the whole population without bias. Non-probability sampling collects data from a selected subset chosen for its convenience or, sometimes, to control and manipulate the data collected.

Types of probability sampling

Random sampling

This type of sampling is completely by chance. Each member of the population has an equal chance of being selected for the sample, and the results of a random sample will be statistically representative of the whole population. 

For example, if you wanted to know how people felt about a new product, you could use a random number generator to select members from a population for the study.

Stratified sampling

Stratified sampling is when the population is split into different subgroups, or strata, based on one or more characteristics. The researcher then randomly selects members from each stratum to represent the population. This allows the researcher to accurately compare data between different groups because it ensures that all subgroups are represented in the sample. 

For example, if you wanted to measure the opinion of people in different age groups, you could divide your population into groups based on age and then take random samples from each stratum.

Cluster sampling

This type of sampling divides the population into clusters or groups and then further takes a sample from each cluster. This method is often used when it isn’t possible to access the entire population. 

For example, if you wanted to measure public opinion on an issue in a large city, it wouldn’t be feasible to survey every single person. Instead, you could divide the city into neighborhoods and take random samples from each one.

Systematic sample

Systematic sampling involves selecting items from a population based on a set pattern or system. This type of sampling is useful when it’s impossible or impractical to create a list of all items in a population. It’s similar to random sampling in that it helps eliminate any bias from the selection process, but it’s more efficient because it requires fewer samples to be taken. 

If a researcher can only select 10 members from a population of 200 people, they could use systematic sampling by selecting every 20th person in the list to eliminate bias.

Types of non-probability sampling

Convenience sampling

This form of sampling involves selecting participants based on availability and willingness to take part. This can lead to volunteer bias, meaning that individuals who are more motivated or have more time may be more likely to participate.

Quota sampling

A method of selecting participants from a larger population to match certain criteria is referred to as quota sampling. For example, market researchers might use quota sampling to select a certain number of individuals within specific age groups.

Judgemental sampling

This technique is also referred to as purposive sampling or authoritative sampling. You can use it to target specific individuals who possess a certain set of qualities like age, ethnicity, or religious beliefs. It can help researchers access important information from people with specific knowledge or experience. 

However, this kind of sampling can also lead to selection bias, which is the distortion of results due to the non-random selection of participants.

Snowball sampling

Snowball sampling is often used to reach individuals who may be difficult to access through traditional means. This type of sampling involves asking participants to refer others who fit the same criteria. It’s often used in social sciences research to identify people within a certain community or social group. For example, researchers may conduct a survey offering a reward to participants who refer their close friends or family and get them to participate.  

While this technique can be useful in reaching underserved or underrepresented populations, it also carries the risk of selection bias.

Advantages of sample data

Cost-effective

Collecting data from a sample is typically less expensive and time-consuming than collecting data from an entire population.  

Higher quality

Collecting data from a smaller subset of a population can often result in higher-quality data when more resources are dedicated to ensuring the accuracy and completeness of the data. 

Feasibility

In some cases, it may be impossible or impractical to collect data from an entire population, making sample data a more feasible option. 

Manageable

Sample data is usually smaller and more manageable than population data, which makes it easier to analyze. 

Reduced sampling bias

With appropriate sampling methods, sample data can be representative of the large population and provide valuable insights for research. 

Disadvantages of using sample data

Generalizability

The quality of the data depends on the quality of the sample selection process. If the sample isn’t representative of the population, it leads to skewed results.

Sampling bias

A sample may not provide a complete picture of an entire population when certain groups are overrepresented or underrepresented in the sample.  

Sampling error

Because sample data is drawn from a subset of a larger population, there is always a risk of sampling error. It occurs when the sample doesn’t accurately represent the larger population, which can lead to inaccurate results.

Statistical power

A small sample size can limit the statistical power of the data analysis, making it more difficult to detect meaningful differences or relationships between studied variables. 

Limited score

Sample data may be limited in scope and may not capture the full range of variables present in an entire population. This can limit the depth and breadth of the findings.

When discussing research and data analysis, it’s important to understand the differences between population and sample data. Here are some key points to consider when distinguishing between the two: 

Population vs. sample

A population is a set of all individuals or objects that share a common characteristic, while a sample is a subset of that population used to draw conclusions about the entire population. 

For example, if you wanted to research the opinions of all people living in the United States, the population would be all citizens in the US, while the sample would be a smaller subset of people surveyed to represent the opinion of the entire population.

Sample vs. population mean

The sample mean is an average of a sample's values, while the population mean is an average of all values in a population. For example, if you’re researching the average income of households in America, the sample mean would be an average of incomes from a smaller group of households selected from the population of all households in the US.

Sample vs. population standard deviation

Standard deviation measures the variation of a set of values from their mean. The sample standard deviation is based on the variation within a sample, while the population standard deviation is based on the variation within a population. 

For example, if you were researching the variation in test scores for students at a particular school, the sample standard deviation would be based on the scores of a smaller subset of students from the school, while the population standard deviation would be based on all scores from every student at the school.

1. Choose the right sampling technique

The most common sampling techniques include random, stratified, convenience, and cluster sampling. Selecting the right technique for your research will depend on your specific needs, resources, goals, and objectives.

2. Decide the sample size

Determining the sample size will vary depending on the goal of your research. Generally speaking, the larger the sample size, the more reliable your results will be. However, there are tradeoffs, such as the cost and resources required to collect data from larger samples.

3. Design an instrument for collecting data

Once you've chosen your sampling technique and decided on the sample size, you'll need to design an instrument for collecting data. This could include surveys, interviews, or experiments. Make sure that the instrument is valid and reliable so that it provides accurate results.

4. Determine a sample frame 

Decide who you’ll include in the sample by selecting the population or subpopulation you want to study. Consider factors like location, age, gender, behavior, and so on when choosing your sample frame.

5. Execute the sample selection process

In this step, you'll select individuals to form your sample. To ensure accuracy, it’s best to use random sampling techniques to guarantee a representative sample.

6. Collect data from a sample

Once you’ve selected the sample, you can begin collecting data. Depending on the method you chose (e.g., survey, interview, experiment), you may need to do some additional steps before you can begin collecting data:

• For example, if you’re collecting data through a survey, you may need to obtain permission to conduct the survey from relevant authorities, such as a workplace or community group.

• If you plan to conduct interviews as your data collection method, ensure your questions are well-formed and that your interviewees are comfortable answering them. Before the interview, you may also want to send a pre-interview questionnaire to participants to collect basic information to make the interview process more efficient.

• Most experiments require a significant amount of planning and preparation to ensure that data is collected in a controlled and systematic manner. Additionally, you may need to consider the ethical implications of conducting the experiment, such as obtaining informed consent from participants and ensuring their safety throughout the experiment.

7. Analyze the data

After you've collected data from the sample, analyze it to find meaningful patterns and trends that you can use to draw conclusions about the population. Remember, since you're working with a sample, your conclusions may not apply to the entire population. 

By following these steps, you can easily collect data from a sample to gain insights about a population without having to analyze all of the data from the population itself. When used correctly, sample data can provide valuable insights that can help shape your research conclusions.

1. Define the population

Before collecting data from a population, it’s important to first clearly define what population you’re looking to collect data from. This definition should be as specific as possible and include any relevant behavioral characteristics (e.g., shopping frequency, product use, or commute options) or demographic characteristics (e.g., age, gender, and geography).

2. Create a comprehensive list

After identifying the population in terms of traits, past experiences, outlooks, or other components, create a comprehensive list of the population you’ll be studying. Depending on the purpose of the study, this could include both people and organizations.

3. Contact population and collect data

Once you’ve defined the population and chosen your sampling method, it’s time to collect data. You can obtain this data by conducting experiments, surveys, or interviews. Make sure to collect feedback from every person or entity on the population list to generate an exhaustive population sample.

4. Analyze the data

After collecting the data, it’s important to analyze it to draw meaningful conclusions about the population. This analysis should include calculating the sample mean and sample standard deviation for the data set, as well as comparing these values to the population mean and population standard deviation.

5. Draw conclusions

Once you’ve analyzed the data, use the results to draw conclusions about the population. Make sure to be as accurate and objective as possible when making claims about the population.

High-quality samples are essential when it comes to research. A high-quality sample will produce accurate and reliable study results. A poor-quality sample can result in incorrect or inexact data. These results can be costly and time-consuming to fix. 

A good-quality sample is representative of the population. That means the sample has similar characteristics as the population in terms of age, gender, race, and other factors. The sample should also be randomly selected so as not to bias the results. In addition, the sample should be of a large enough size to be statistically significant.

How to select a high-quality sample

Choose a probability sampling method

Random selection is the most important part of choosing a high-quality sample. You want to ensure that the sample truly represents the population and that no bias has been introduced. You can do this through methods such as random sampling, stratified sampling, cluster sampling, and systematic sampling. 

Monitor selection process

You should monitor the selection process to ensure that no bias has been introduced during the selection process. You should also make sure that the sample size is large enough to be statistically significant. 

Test for accuracy

You should test the accuracy of your sample by comparing it to the population data. Compare the sample mean vs. population mean, sample vs. population standard deviation, and other factors. If there are any discrepancies between the two, then the sample may not be representative of the population and should be re-evaluated.

By following these steps, you can ensure that your sample is quality and that it correctly reflects the population and produces precise and accurate results.

Using sample and population data can be beneficial in many ways. For example, using sample data allows researchers to make more efficient use of resources while still being able to conclude the population. Additionally, sample data is useful in making statistical inferences about a population, such as the mean or standard deviation. 

On the other hand, population data provides an accurate representation of the whole population, which can be beneficial when researchers need detailed information. 

To ensure accurate and representative data, researchers must understand the differences between populations and weigh the advantages and risks of each sampling technique. By understanding the difference between population and sample data, researchers can gain valuable insights about their target group and use these insights to make informed decisions.