Sample: Definition, Methodologies, Types, formula, and Examples | QuestionPro (2023)

How often do researchers look for the right survey respondents, either for a market research study or an existing survey in the field? The sample or the respondents of this research may be selected from a set of customers or users that are known or unknown. You may often know your typical respondent profile but don’t have access to the respondents to complete your research study. At such times, researchers and research teams reach out to specialized organizations to access their panel of respondents or buy respondents from them to complete research studies and surveys. These could be general population respondents that match demographic criteria or respondents based on specific criteria. Such respondents are imperative to the success of research studies.

What is a sample?

Definition: A sample is defined as a smaller set of data that a researcher chooses or selects from a larger population by using a pre-defined selection method. These elements are known as sample points, sampling units, or observations. Creating a sample is an efficient method of conducting research. In most cases, it is impossible or costly and time-consuming to research the whole population. Hence, examining the sample provides insights that the researcher can apply to the entire population.

For example, if a cell-phone manufacturer wants to conduct a feature research study among students in US Universities. If the researcher is looking for features that the students use, features they would like to see, and the price that they are willing to pay, an in-depth research study has to be conducted. This step is imperative to understand the features that need development, the features that require an upgraded, pricing of the device, and the go-to-market strategy.

In 2016/17 alone, there were 24.7 million students enrolled in universities across the US. It is impossible to research all of these students; the time spent would create the new device redundant, and the money spent on development would render the study useless. Creating a sample of universities by geographical location and further creating a sample of these students from these universities provides a large enough number of students for research.

Select your respondents

(Video) Types of Sampling Methods (4.1)

Typically, the population for market research is enormous. Making an enumeration of the whole population is practically impossible. The sample usually represents a manageable size from this population. Researchers then collect data from these samples in the form of surveys, polls, and questionnaires, and extrapolates this data analysis to the broader community.

Sample: Definition, Methodologies, Types, formula, and Examples | QuestionPro (1)

Types of samples: Sample selection methodologies with examples

The process of deriving a sample is called a sampling method. Sampling forms an integral part of the research design as this method derives the quantitative data and the qualitative data that can be collected as part of a research study. Sampling methods are characterized into two distinct approaches: probability sampling and non-probability sampling.

Probability sampling methodologies with examples

Probability sampling is a method of deriving a sample where the objects are selected from a population-based on the theory of probability. This method includes everyone in the population, and everyone has an equal chance of being selected. Hence, there is no bias whatsoever in this type of sample. Each person in the population can subsequently be a part of the research. The selection criteria are decided at the outset of the market research study and form an important component of research.

Probability sampling can be further classified into four distinct types of samples. They are:

(Video) Sampling: Simple Random, Convenience, systematic, cluster, stratified - Statistics Help

  • Simple random sampling: The most straightforward way of selecting a sample is simple random sampling. In this method, each member has an equal chance of being a part of the study. The objects in this sample population are chosen purely on a random basis, and each member has the same probability of being selected. For example, if a university dean would like to collect feedback from students about their perception of the teachers and level of education, all 1000 students in the University could be a part of this sample. Any 100 students can be selected at random to be a part of this sample.
  • Cluster sampling: Cluster sampling is a type of sampling method where the respondent population is divided into equal clusters. Clusters are identified and included in a sample based on defining demographic parameters such as age, location, sex, etc. This makes it extremely easy for a survey creator to derive practical inferences from the feedback. For example, if the FDA wants to collect data about adverse side effects from drugs, they can divide the mainland US into distinctive clusters, like states. Research studies are then administered to respondents in these clusters. This type of generating a sample makes the data collection in-depth and provides easy to consume and act upon, insights.
  • Systematic sampling: Systematic sampling is a sampling method where the researcher chooses respondents at equal intervals from a population. The approach to select the sample is to pick a starting point and then pick respondents at a pre-defined sample interval. For example, while selecting 1,000 volunteers for the Olympics from an application list of 10,000 people, each applicant is given a count of 1 to 10,000. Then starting from 1 and selecting each respondent with an interval of 10, a sample of 1,000 volunteers can be obtained.
  • Stratified random sampling: Stratified random sampling is a method of dividing the respondent population into distinctive but pre-defined parameters in the research design phase. In this method, the respondents don’t overlap but collectively represent the whole population. For example, a researcher looking to analyze people from different socioeconomic backgrounds can distinguish respondents into their annual salaries. This forms smaller groups of people or samples, and then some objects from these samples can be used for the research study.

Non-probability sampling methodologies with examples

The non-probability sampling method uses the researcher’s discretion to select a sample. This type of sample is derived mostly from the researcher’s or statistician’s ability to get to this sample. This type of sampling is used for preliminary research where the primary objective is to derive a hypothesis about the topic in research. Here each member does not have an equal chance of being a part of the sample population, and those parameters are known only post-selection to the sample.

We can classify non-probability sampling into four distinct types of samples. They are:

  • Convenience sampling: Convenience sampling, in easy terms, stands for the convenience of a researcher accessing a respondent. There is no scientific method of deriving this sample. Researchers have nearly no authority over selecting the sample elements, and it’s purely done on the basis of proximity and not representativeness.This non-probability sampling method is used when there are time and cost limitations in collecting feedback. For example, researchers that are conducting a mall-intercept survey to understand the probability of using a fragrance from a perfume manufacturer. In this sampling method, the sample respondents are chosen purely on their proximity to the survey desk and their willingness to participate in the research.
  • Judgemental/purposive sampling: The judgemental or purposive sampling method is a method of developing a sample purely on the basis and discretion of the researcher purely on the basis of the nature of study along with his/her understanding of the target audience. In this sampling method, people who only fit the research criteria and end objectives are selected, and the remaining are kept out.For example, if the research topic is understanding what University a student prefers for Masters, if the question asked is “Would you like to do your Masters?” anything other than a response, “Yes” to this question, everyone else is excluded from this study.
  • Snowball sampling: Snowball sampling or chain-referral sampling is defined as a non-probability sampling technique in which the samples have traits that are rare to find. This is a sampling technique, in which existing subjects provide referrals to recruit samples required for a research study.For example, while collecting feedback about a sensitive topic like AIDS, respondents aren’t forthcoming with information. In this case, the researcher can recruit people with an understanding or knowledge of such people and collect information from them or ask them to collect information.
  • Quota sampling: Quota sampling is a method of collecting a sample where the researcher has the liberty to select a sample based on their strata. The primary characteristic of this method is that two people cannot exist under two different conditions. For example, when a shoe manufacturer would like to understand from millenials their perception of the brand with other parameters like comfort, pricing, etc. It selects only females who are millennials for this study as the research objective is to collect feedback about women’s shoes.

How to determine a sample size

As we have learned above, the right sample size is essential for the success of data collection in a market research study. But is there a correct number for sample size? What parameters decide the sample size? What are the distribution methods of the survey? To understand all of this and make an informed calculation of the right sample size, it is first essential to understand four important variables that form the basic characteristics of a sample. They are:

  • Population size: The population size is all the people that can be considered for the research study. This number, in most cases, runs into huge amounts. For example, the population of the United States is 327 million. But in market research, it is impossible to consider all of them for the research study.
  • The margin of error (confidence interval): The margin of error is depicted by a percentage that is a statistical inference about the confidence of what number of the population depicts the actual views of the whole population. This percentage helps towards the statistical analysis in selecting a sample and how much error in this would be acceptable.
  • Confidence level: This metric measures where the actual mean falls within a confidence interval. The most common confidence intervals are 90%, 95%, and 99%.
  • Standard deviation: This metric covers the variance in a survey. A safe number to consider is .5, which would mean that the sample size has to be that large.

Calculating sample size

To calculate the sample size, you need the following parameters.

  • Z-score: The Z-score value can be found, here.
  • Standard deviation
  • Margin of error
  • Confidence level

To calculate use the sample size, use this formula:

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Sample Size = (Z-score)2 * StdDev*(1-StdDev) / (margin of error)2

Consider the confidence level of 90%, standard deviation of .6 and margin of error, +/-4%

((1.64)2 x .6(.6)) / (.04)2

( 2.68x .0.36) / .0016

.9648 / .0016

(Video) Percent Concentration Calculations with Easy Trick and Example - Part- 1 हिंदी में (%w/w, %v/v,%w/v)


603 respondents are needed and that becomes your sample size.

Try our sample size calculator for give population, margin of error and confidence level.

Sampling advantages

As shown above, there are many advantages to sampling. Some of the most significant advantages are:

  • Reduced cost & time: Since using a sample reduces the number of people that have to be reached out to, it reduces cost and time. Imagine the time saved between researching with a population of millions vs. conducting a research study using a sample.
  • Reduced resource deployment: It is obvious that if the number of people involved in a research study is much lower due to the sample, the resources required are also much less. The workforce needed to research the sample is much less than the workforce needed to study the whole population.
  • Accuracy of data: Since the sample is indicative of the population, the data collected is accurate. Also, since the respondent is willing to participate, the survey dropout rate is much lower, which increases the validity and accuracy of the data.
  • Intensive & exhaustive data: Since there are lesser respondents, the data collected from a sample is intense and thorough. More time and effort is given to each respondent rather than having to collect data from a lot of people.
  • Apply properties to a larger population: Since the sample is indicative of the broader population, it is safe to say that the data collected and analyzed from the sample can be applied to the larger population, and it would hold true.

To collect accurate data for research, filter bad panelists, and eliminate sampling bias by applying different control measures. If you need any help with arranging a sample audience for your next market research project, get in touch with us on We have more than 22 million panelists across the world!

(Video) Sampling 06: Non-Probability Sampling

Select your respondents


What is sample methodology? ›

Sampling is a method that allows researchers to infer information about a population based on results from a subset of the population, without having to investigate every individual.

What are the 5 types of samples? ›

There are five types of sampling: Random, Systematic, Convenience, Cluster, and Stratified.

What is sampling method and its types? ›

In statistics, sampling is a method when researchers determine a representative segment of a larger population that is then used to conduct a study. Sampling generally comes in two forms — probability sampling and non-probability sampling.

What are the 4 sampling strategies? ›

Four main methods include: 1) simple random, 2) stratified random, 3) cluster, and 4) systematic. Non-probability sampling – the elements that make up the sample, are selected by nonrandom methods. This type of sampling is less likely than probability sampling to produce representative samples.

What are 3 reasons to use samples? ›

Samples are used to make inferences about populations. Samples are easier to collect data from because they are practical, cost-effective, convenient, and manageable.

What are the types of methodology? ›

The three types of methodology used by researchers are qualitative, quantitative, and mixed methods.

What sample means Example? ›

What is the sample mean? A sample mean is an average of a set of data . The sample mean can be used to calculate the central tendency, standard deviation and the variance of a data set. The sample mean can be applied to a variety of uses, including calculating population averages.

What is the best type of sample? ›

Simple random sampling: One of the best probability sampling techniques that helps in saving time and resources, is the Simple Random Sampling method. It is a reliable method of obtaining information where every single member of a population is chosen randomly, merely by chance.

What are 5 types of sampling bias? ›

What are some types of sampling bias? Some common types of sampling bias include self-selection bias, nonresponse bias, undercoverage bias, survivorship bias, pre-screening or advertising bias, and healthy user bias.

How do you sample? ›

The general approach to sampling involves taking a portion of sound from your audio track and processing it through your sampler or Digital Audio Workstation. You'll then chop it up, loop it, pitch it and or arrange it in an entirely new way to create a brand new sound for your song.

What are six sampling methods? ›

6 Techniques for Market Research Sampling
  1. True Random Sampling.
  2. Systematic Sampling.
  3. Stratified Sampling.
  4. Quota Sampling.
  5. Cluster Sampling.
  6. Area Sampling.
  7. Choosing the Right Sampling Technique Your Market Research.

What is sampling and its types PDF? ›

This article review the sampling techniques used in research including Probability sampling techniques, which include simple random sampling, systematic random sampling and stratified random sampling and Non-probability sampling, which include quota sampling, self-selection sampling, convenience sampling, snowball ...

What is 3 class sampling plan? ›

A Three-class sampling plan is defined by (n,c,m,M) with an additional specification limit M> m; the lot is also rejected if at least one of the n measured log-concentrations is larger than M. A Three-class sampling plan protects better against unacceptable lots than the underlying Two-class sampling plan.

What are the 5 steps to follow in sampling? ›

The five steps to sampling are:
  1. Identify the population.
  2. Specify a sampling frame.
  3. Specify a sampling method.
  4. Determine the sample size.
  5. Implement the plan.
25 May 2022

What are the 4 types of sampling bias? ›

Types of Sampling Bias
  • Observer Bias. Observer bias occurs when researchers subconsciously project their expectations on the research. ...
  • Self-Selection/Voluntary Response Bias. ...
  • Survivorship Bias. ...
  • Recall Bias.
28 Oct 2021

What is the formula for random sampling? ›

The Formula of Random Sampling

(N-n/N-(n-1)). Here P is a probability, n is the sample size, and N represents the population. Now if one cancels 1-(N-n/n), it will provide P = n/N.

What is the purpose of a sample? ›

In research terms a sample is a group of people, objects, or items that are taken from a larger population for measurement. The sample should be representative of the population to ensure that we can generalise the findings from the research sample to the population as a whole.

Why is a sample useful? ›

Samples are used to make inferences about populations. Samples are easier to collect data from because they are practical, cost-effective, convenient, and manageable.

What are the purpose of sampling? ›

The primary goal of sampling is to create a representative sample, one in which the smaller group (sample) accurately represents the characteristics of the larger group (population). If the sample is well selected, the sample will be generalizable to the population. There are many ways to obtain a sample.

What is the 4 parts of methodology? ›

... research methods are comprised of four main parts: (i) slums conceptualisation, (ii) OBIA ruleset development, (iii) ruleset implementation, (iv) accuracy and uncertainty measurement. Our methodology is shown in Figure 2, and the detailed process is described in the following paragraph.

What are the 3 parts of methodology? ›

Abstract. Chapter 3 consists of three parts: (1) Purpose of the study and research design, (2) Methods, and (3) Statistical Data analysis procedure.

What is basic methodology? ›

In its most common sense, methodology is the study of research methods. However, the term can also refer to the methods themselves or to the philosophical discussion of associated background assumptions. A method is a structured procedure for bringing about a certain goal.

What are the 7 components of research methodology? ›

A research report has seven components:
  • Abstract or Summary.
  • Introduction.
  • Review of Literature.
  • Methods.
  • Results.
  • Conclusions and Discussion.
  • References.

How many types of methods are there? ›

There are three main types of methods: interface methods, constructor methods, and implementation methods.

What is a sample of data? ›

In data analysis, sampling is the practice of analyzing a subset of all data in order to uncover the meaningful information in the larger data set.

What is an example of sample data? ›

The data are the number of books students carry in their backpacks. You sample five students. Two students carry three books, one student carries four books, one student carries two books, and one student carries one book. The numbers of books (three, four, two, and one) are the quantitative discrete data.

What stands for sample mean? ›

The sample mean is a random variable; as such it is written ˉX, and ˉx stands for individual values it takes. As a random variable the sample mean has a probability distribution, a mean μˉX, and a standard deviation σˉX.

Which sample size is best? ›

A good maximum sample size is usually 10% as long as it does not exceed 1000. A good maximum sample size is usually around 10% of the population, as long as this does not exceed 1000. For example, in a population of 5000, 10% would be 500. In a population of 200,000, 10% would be 20,000.

What is sample select? ›

Judgement sampling, commonly referred to as purposeful or selective sampling, relies on the judgement and practical knowledge of the researcher to identify and select participants. A framework for selection can be developed from variables identified in the literature, combined with practical knowledge of the phenomena.

What is sample size in research? ›

What is sample size and why is it important? Sample size refers to the number of participants or observations included in a study. This number is usually represented by n. The size of a sample influences two statistical properties: 1) the precision of our estimates and 2) the power of the study to draw conclusions.

What are the 8 common types of bias? ›

Here are eight common biases affecting your decision making and what you can do to master them.
  • Survivorship bias. Paying too much attention to successes, while glossing over failures. ...
  • Confirmation bias. ...
  • The IKEA effect. ...
  • Anchoring bias. ...
  • Overconfidence biases. ...
  • Planning fallacy. ...
  • Availability heuristic. ...
  • Progress bias.

What are the 6 types of bias? ›

We've handpicked six common types of bias and share our tips to overcome them:
  • Confirmation bias. Confirmation bias is when data is analysed and interpreted to confirm hypotheses and expectations. ...
  • The Hawthorne effect. ...
  • Implicit bias. ...
  • Expectancy bias. ...
  • Leading Language. ...
  • Recall bias.

What are the 3 types of bias examples? ›

Confirmation bias, sampling bias, and brilliance bias are three examples that can affect our ability to critically engage with information.

What are the steps in sample? ›

There are 4 key steps to select a simple random sample.
  1. Step 1: Define the population. Start by deciding on the population that you want to study. ...
  2. Step 2: Decide on the sample size. Next, you need to decide how large your sample size will be. ...
  3. Step 3: Randomly select your sample. ...
  4. Step 4: Collect data from your sample.
28 Aug 2020

How do you write sampling? ›

You need to: (1) describe what you are studying, including the units involved in your sample and the target population; (2) explain the types of sampling technique available to you; (3) state and describe the sampling strategy you used; and (4) justify your choice of sampling strategy.

How do you plan a sample? ›

The steps involved in developing a sampling plan are:
  1. identify the parameters to be measured, the range of possible values, and the required resolution.
  2. design a sampling scheme that details how and when samples will be taken.
  3. select sample sizes.
  4. design data storage formats.
  5. assign roles and responsibilities.

What are the different types of sampling operations? ›

There are three types of sampling techniques: Impulse sampling. Natural sampling. Flat Top sampling.

What is sampling method of collection? ›

Three popular methods of blood collection are: Arterial Sampling. Venipuncture Sampling. Fingerstick Sampling.

What is the first step in sampling process? ›

The first stage in the sampling process is to clearly define target population. Population is commonly related to the number of people living in a particular country. A sampling frame is a list of the actual cases from which sample will be drawn. The sampling frame must be representative of the population.

What is sampling design PPT? ›

1. Sampling Design.  The process of obtaining information from a subset (sample) of a larger group (population)  The results for the sample are then used to make estimates of the larger group  Faster and cheaper than asking the entire population  Two keys 1.

How many types of sampling distribution are there? ›

This concept is further classified into 3 types - Sampling Distribution of mean, proportion, and T-Sampling. Sampling Distribution is immensely significant for generating accurate data that can otherwise be hampered if repeated sampling does not take place.

What is M in sampling? ›

'M' is the concentration in the sample above which the lot is automatically rejected. Defining M can increase stringency of the sampling plan, as can be seen in Table 1. Table 1 . Comparison of Presence/absence and Concentration-based Sampling Plans.

What is a 2-class sampling plan? ›

The 2-class attributes sampling plan simply classifies each sample unit as acceptable (nondefective) or unacceptable (defective).

What is a bulk sample? ›

Sample 1. Bulk sample means a collection of representative mineralized material whose location, geologic character and metal assay content can be determined, and then used for metallurgical or geotechnical testing purposes.

What are the samples in research? ›

In research terms a sample is a group of people, objects, or items that are taken from a larger population for measurement. The sample should be representative of the population to ensure that we can generalise the findings from the research sample to the population as a whole.

What are samples in the laboratory? ›

Medical: A laboratory specimen is a sample of a medical patient's tissue, fluid, or other material derived from the patient used for laboratory analysis to ... (analytical chemistry) A sample of a material to be tested or analyzed that is prepared from a gross sample and retains the latter's composition.

What are types of biological samples? ›

Biological samples, also known as biological materials or biological specimens, include various samples such as blood, urine, tissue, cells, saliva and many others.

What are samples of data? ›

Data sampling is a statistical analysis technique used to select, manipulate and analyze a representative subset of data points to identify patterns and trends in the larger data set being examined.

Whats a sample mean? ›

The sample mean is a statistic obtained by calculating the arithmetic average of the values of a variable in a sample. If the sample is drawn from probability distributions having a common expected value, then the sample mean is an estimator of that expected value. Definition.

What is a good sample? ›

What makes a good sample? A good sample should be a representative subset of the population we are interested in studying, therefore, with each participant having equal chance of being randomly selected into the study.

What is sample instrument? ›

A sampler is an electronic or digital musical instrument which uses sound recordings (or "samples") of real instrument sounds (e.g., a piano, violin, trumpet, or other synthesizer), excerpts from recorded songs (e.g., a five-second bass guitar riff from a funk song) or found sounds (e.g., sirens and ocean waves).

What is sample equipment? ›

Sampling equipment is equipment which is used to remove small amounts of something for analysis and monitoring. Special sampling equipment is used to get a representative sample of the liquid contained in a high-pressure storage tank.

What is the importance of sample collection? ›

It is a foundational principle for any laboratory test procedure that the value of the test is compromised or even negated by using specimens that have not been properly collected, labelled, handled or stored prior to and during the testing process.

What are primary samples? ›

The primary sample or specimen is a set of one or more parts initially taken from an object. In some countries, the term “specimen” is used instead of primary sample (or a subsample of it), which is the sample prepared for sending to, or as received by, the laboratory and which is intended for examination.

What are the 4 types of specimen preparation? ›

Specimen Preparation
  • Focused Ion Beam.
  • Transmission Electron Microscopy.
  • Atom Probe Tomography.
  • Electron Microscope.

What are primary human samples? ›

Human primary cells are cells isolated directly from human tissues, including blood and bone marrow. They are established as an important tool for in vitro cell-based assays or for generating in vivo models, such as xenograft or humanized mice.

What are the 10 examples of data? ›

10 data types
  • Integer. Integer data types often represent whole numbers in programming. ...
  • Character. In coding, alphabet letters denote characters. ...
  • Date. This data type stores a calendar date with other programming information. ...
  • Floating point (real) ...
  • Long. ...
  • Short. ...
  • String. ...
  • Boolean.
21 Jul 2021

Which is primary data? ›

Primary data refers to the first hand data gathered by the researcher himself. Secondary data means data collected by someone else earlier. Surveys, observations, experiments, questionnaire, personal interview, etc. Government publications, websites, books, journal articles, internal records etc.

What are the 4 types of random sampling? ›

There are four primary, random (probability) sampling methods – simple random sampling, systematic sampling, stratified sampling, and cluster sampling.


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