Name: choosing samples for reliable results
Uploaded: 2024-12-05T18:31:54.000Z
Duration: 1 min 23 s
Channel: JoVE

일반적인 표본추출 방법은 무작위 표본추출, 판단 표본추출, 체계적 표본추출, 계층화 표본추출, 군집 표본추출입니다. 
무작위 표본추출에서 표본은 선호도가 없는 모집단에서 개인을 무작위로 선택하여 얻어지며, 각 개인은 선택될 확률이 동일합니다.
반대로, 판단 표본추출은 비무작위 프로세스입니다. 여기에서 모집단에 대해 사용 가능한 정보를 기반으로 표본이 선택됩니다.
체계적 표본추출은 일정한 간격으로 모집단에서 개인을 선택하는 방법입니다. 예를 들어, 12명의 모집단에서 4명의 표본 크기를 생성하기 위해 시작점은 1과 표본 추출 구간 사이에서 무작위로 선택됩니다. 따라서 모든 3번째 구성원을 선택하여 4명의 표본을 만듭니다.
계층화된 표본추출에서 모집단은 개인이 공유하는 특성에 따라 하위 그룹 또는 계층으로 나뉩니다. 그런 다음 각 하위 그룹에서 비례적으로 개인을 선택하여 분석을 위한 최종 샘플을 구성합니다.
마찬가지로, 군집 표본추출에는 모집단을 하위 그룹 또는 군집으로 나누는 것도 포함됩니다. 그런 다음 평가를 위해 몇 개의 클러스터를 무작위로 선택합니다.

표본추출 계획

표본추출은 분석 화학에서 중요한 단계로, 연구자들이 대규모 모집단에서 대표적 자료를 수집할 수 있도록 합니다. 일반적인 표본추출 방법에는 무작위, 판단적, 체계적, 계층적 및 클러스터 표본추출이 있습니다.

무작위 표본추출은 모집단의 각 구성원이 표본에 선택될 확률이 동일한 방법입니다. 여기에는 종종 난수 생성기 또는 복권 유형의 방법을 사용하여 개인을 무작위로 선택하는 것이 포함됩니다. 예를 들어, 폴리머 시트의 특성을 분석할 때 무작위 표본추출은 시트를 1cm x 1cm의 동일한 섹션으로 나눈 다음 난수 표를 사용하여 분석을 위해 무작위로 10개의 섹션을 선택하여 사용할 수 있습니다. 이렇게 하면 시트 전체에서 편향되지 않은 표본이 선택됩니다. 무작위 표본추출은 편향을 최소화하고 전체 모집단을 정확하게 나타내는 표본을 생성하는 데 도움이 됩니다.

의도적 또는 선택적 표본추출이라고도 하는 판단적 표본추출은 연구에 가장 적합하다고 여겨지는 개인이나 표본을 선택하기 위해 연구자의 판단이나 전문성에 의존하는 비확률 방법입니다. 예를 들어, 연구자가 물고기에서 폴리염소비페닐(PCB)의 생물 축적을 연구하고 있다고 가정해 보겠습니다. 이 경우, 그들은 더 작거나 건강에 해로워 보이는 것과 같은 특정 기준을 충족하는 물고기만 선택적으로 표본을 추출할 수 있습니다. 이 방법은 규제 기관에서 수집하는 표본을 정의하기 위해 특정 기준을 요구할 때 자주 사용됩니다.

체계적 표본 추출은 무작위로 시작점을 선택한 후 개체군에서 n번째 개체를 선택하는 것을 포함합니다. 예를 들어, 환경 연구에서 체계적 표본 추출은 호수를 격자로 나누고 각 섹션에서 정기적으로 표본을 채취하여 호수 전체에 걸쳐 공간적 범위를 확보하여 표본을 수집하는 데 사용할 수 있습니다. 이 접근 방식은 물 속 산소 분포와 같은 공간적 추세를 포함하는 연구에 도움이 됩니다.

계층적 표본 추출은 연구와 관련된 특정 특성을 기반으로 개체군을 별개의 하위 그룹 또는 계층으로 나누는 것을 포함합니다. 그런 다음 개체군에서의 표현에 비례하여 각 계층에서 표본을 무작위로 선택합니다. 예를 들어, 도시 대기의 입자 물질을 연구할 때 계층적 표본 추출은 개체군을 입자 크기 범주(예: 미세, 거칠음)로 나누어 사용할 수 있습니다. 그런 다음 각 입자 크기 그룹에서 표본을 채취하여 전체 오염 수준에 대한 기여도를 평가합니다. 이 방법은 각 하위 그룹 내에서 보다 정확한 분석을 제공하고 표본추출 오류를 줄입니다.

클러스터 표본추출은 인구를 클러스터 또는 그룹으로 나누는 것을 포함하며, 이상적으로는 인구의 미니 표현입니다. 몇몇 클러스터는 무작위로 선택되고 선택된 클러스터 내의 모든 사람이 표본추출됩니다. 이 방법은 일반적으로 물류적 제약으로 인해 표본추출 장소 수가 제한되는 대규모 연구에서 사용됩니다. 예를 들어 지하수 오염에 대한 연구에서는 지리적 경계를 기준으로 지역을 클러스터로 나눈 다음 사용 가능한 모든 우물을 표본추출하기 위해 몇몇 클러스터(지역)를 무작위로 선택할 수 있습니다.

샘플링은 분석 화학에서 중요한 단계로, 연구원들이 많은 모집단에서 대표 데이터를 수집할 수 있도록 합니다. 일반적인 샘플링 방법 ...

Education

교육

JoVE Core

Analytical Chemistry

분석 화학

Unit 1

제1단원

Method Development and Sampling Techniques

분석법 개발 및 시료 채취 기술

method-development-and-sampling-techniques

KEY TERMS AND CONCEPTS

주요 용어 및 개념

Sampling Plans

choosing samples for reliable results

Sampling is a key step in analytical chemistry. It helps researchers collect data that represents a larger population. The main sampling methods in this topic are random, judgmental, systematic, stratified, and cluster sampling.

Random sampling gives each member of the population an equal chance of being chosen. Researchers often use a random number generator or a lottery-style method. For example, a polymer sheet can be divided into 1 cm x 1 cm sections, and 10 sections can be selected at random for analysis. This helps reduce bias and supports a sample that reflects the whole population.

Judgmental sampling is also called purposive or selective sampling. It depends on the researcher&amp;#39;s judgment to choose samples that fit the study. For example, a researcher studying bioaccumulation of PCBs in fish may choose smaller fish or fish that appear unhealthy. Regulatory agencies may also require specific criteria for this kind of sampling.

Systematic sampling uses a random starting point and then selects every n th individual. It can also be used in environmental studies with a grid, such as sampling a lake at regular intervals. This method helps provide spatial coverage across the lake. It is useful when studying spatial trends, such as oxygen distribution in water.

Stratified sampling divides a population into strata, or subgroups, based on a feature linked to the study. Samples are then randomly taken from each stratum in proportion to its size in the population. For example, particulate matter in urban air can be grouped by particle size, such as fine and coarse particles. This approach can improve precision within each subgroup and reduce sampling error.

Cluster sampling divides the population into clusters, or groups that can act as mini-representations of the whole. A few clusters are randomly selected, and everyone within those clusters is sampled. This method is often used in large studies when the number of sampling sites must be limited. For example, a groundwater contamination study may divide a region into geographic clusters and then sample all available wells in the chosen clusters.

Choosing Samples for Reliable Results

development of analytical methods

Analytical Methods: Technique to Protocol

Analytical methods follow a clear path from technique to protocol. In analytical chemistry, a technique is the scientific principle used to explain a chemical measurement. A method applies that technique to a sample of interest. The next steps are procedure and protocol. A procedure gives the directions for carrying out the analysis with an analytical method. A protocol is the detailed set of guidelines for that procedure, and it should be followed closely to get the desired results. <br...

quality control

Quality Control Charts and Lab Records

Quality control charts, proficiency testing, and lab records are key parts of quality control in a laboratory. These steps help keep a system under statistical control. They also help track data, show trends, and spot variations that may affect the accuracy of an analysis. One common tool is a quality control chart. This chart plots one or more analytical characteristics over time. The measured values are taken at different times during the analysis and compared with the known value of...

quality assurance

Quality Checks in Analytical Testing

Quality assurance in analytical testing brings together the checks that help a system perform properly. It includes quality control, quality assessment, and internal corrective measures. These parts work in a cycle to support reliable results. Quality control happens before and during the analysis. Quality assessment takes place during and after the investigation. Internal corrective measures are then based on the results of post-analysis quality assessment, or they may be applied before a new...

data validation

How Analytical Methods Are Checked

Method validation checks whether an analytical chemistry method gives reliable results. It is especially important when the same method is used with different sample matrices or when the procedure is changed. Validation helps show that the method still meets acceptable standards in each case. Several key checks are used in method validation. Specificity means the method can measure the target analyte without interference from other substances. Linearity means the result changes in direct...

qualitative analysis

Classical and Instrumental Sample ID

Qualitative analysis identifies the elements, ions, or compounds in an unknown sample. It is the first step in the hierarchy of analytical goals. That makes it the starting point for scientific study before quantitative analysis or other forms of analysis. Two main approaches are used in qualitative analysis: classical methods and instrumental methods. Classical methods depend on the visible or sensory result of a chemical reaction, such as a color change, a precipitate, or even a smell. These...

quantitative analysis

Measuring Analyte Concentration

Quantitative analysis measures the amount of a specific substance, called the analyte, in a sample. If the sample composition is unknown, qualitative analysis comes first. That step identifies the components so the correct substances can be measured during the quantitative phase. This method depends on two key measurements. Scientists measure the sample quantity and also a property that is proportional to the amount of analyte. Together, these measurements help determine the analyte...

instrument calibration

Calibrating Lab Instruments for Accurate Results

Calibration helps lab instruments produce accurate and consistent results. It is important in manufacturing, healthcare, testing laboratories, and scientific research. Each instrument needs a calibration process that matches its design and function. This process improves data accuracy and helps results stay reliable. An analytical balance measures mass and needs regular calibration to stay precise. It is calibrated by comparing its readings with known standard weights. These weights act as...

glassware calibration

Calibrating Lab Glassware for Accurate Volume

Calibrating lab glassware helps students measure liquids accurately in the analytical laboratory. It reduces volume errors and supports consistent results across measurements. This matters when using volumetric flasks, pipettes, burettes, and other tools that depend on precise volume readings. Volumetric flasks are used to prepare aqueous solutions with a precise final volume. They have a calibration line on the neck. To calibrate one, fill it with distilled water until the meniscus, the...

standard solutions

Preparing Standard Solutions in the Lab

Standard solutions are prepared to have a precisely known concentration or composition. In analytical chemistry, this accuracy is important because it supports reliable results. A primary standard is a highly pure, stable substance with a high molar mass. It is fully soluble in water, which is the most commonly used solvent in analytical chemistry. A primary standard solution can be used to standardize a secondary standard. Secondary standards have known concentrations, but they are usually...

blank solutions

Blank Solutions in Analytical Testing

Blank solutions are used in analytical testing to show the background signal before a sample is measured. A blank solution does not contain the analyte, which is the substance of interest being tested or measured. It is usually made with the same reagents and procedure as the sample solution, but without the analyte. The main purpose of a blank solution is to control for background interference and contamination. Reagents, solvents, or lab equipment can sometimes create a detectable signal on...

sampling methods: overview

How Sampling Shapes Lab Results

Sampling shapes lab results by determining how a smaller sample represents a larger population. In analytical chemistry, testing an entire population is often impractical or impossible, so samples are collected to make inferences about the whole group. The sampling method is the process used to choose individuals or items for that sample. Common sampling methods include random, judgemental, systematic, stratified, and cluster sampling. Each method can affect the quality of the data in a...

sampling methods: sample types

Sampling Materials in Solid, Liquid, Gas

Sampling materials are grouped as solid, liquid, or gas. The type of sample helps decide the right collection method. Solid samples can include sediments from water bodies, soil, metals, and biological tissues. Sediment sampling from water bodies can be done in two common ways. Grab sampling uses a device to collect a discrete sample from the bottom with minimal disturbance. These samples may not show the full area because conditions can vary from place to place. Piston coring collects a...

sampling plans

Sampling is a key step in analytical chemistry. It helps researchers collect data that represents a larger population. The main sampling methods in this topic are random, judgmental, systematic, stratified, and cluster sampling. Random sampling gives each member of the population an equal chance of being chosen. Researchers often use a random number generator or a lottery-style method. For example, a polymer sheet can be divided into 1 cm x 1 cm sections, and 10 sections can be selected at...

sample preparation for analysis: overview

Preparing Samples by State and Form

Sample preparation depends on the state and form of the sample before analysis. It helps make the sample ready for accurate measurement. The main goal is to extract the analyte, which is the substance being measured, and remove parts that could interfere with the analysis. Solid samples often need the most handling. Large solids are usually ground, crushed, or milled to make them smaller and increase surface area. The sample is then sieved and mixed so it has a uniform composition. After that,...

sample preparation for analysis: advanced techniques

sample-preparation-for-analysis-advanced-techniques

Preparing Complex Samples for Analysis

Preparing complex samples for analysis often requires special digestion and fusion methods. Samples with inorganic or organic material can be hard to dissolve or break down. Common sample preparation methods include acid digestion, fusion, dry ashing, and wet digestion. These steps help turn difficult samples into forms that can be tested reliably and again with similar results. Acid digestion is often used for inorganic materials that do not dissolve in water. It is useful for soil and...

sample handling

Sample Transport and Storage Basics

Sample transport and storage help keep specimens intact before testing. Moving a sample from the collection point to the laboratory requires careful handling. The sample should be sealed well and clearly labeled. These steps help prevent cross-contamination and support reliable results. Temperature control is also important during transport. Some samples travel in insulated containers, cool packs, or refrigerated vehicles so they stay within the needed temperature range. After the samples...

contaminants and errors

Sampling Errors in Sample Preparation

Sampling errors in sample preparation can affect the accuracy of laboratory results. Two common problems are concentration bias from poor sample splitting and contamination from reducing particle size by grinding or homogenization. Recognizing these errors helps make analysis more reliable. The number of samples also matters when a target population follows a normal distribution. In that case, the sample size ns can be found with a formula that uses the t-value for the chosen confidence level,...

key terms and concepts

Learn how random, judgmental, systematic, stratified, and cluster sampling are used in analytical chemistry to collect representative data.

Choosing Samples for Reliable Results | JoVE K12

analytical chemistry

JoVE Core Analytical Chemistry simplifies complex chemical principles by breaking them down into clear, engaging animations, making topics from SI Units to NMR spectroscopy more accessible and straightforward. Additionally, the scientist-in-action videos highlight the application of these concepts in real-world research conducted in laboratories globally.

Choosing Samples for Reliable Results

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