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

一般的なサンプリング方法は、ランダム、判断、系統的、層別、およびクラスター サンプリングです。 
ランダムサンプリングでは、サンプルは、選好されずに母集団から個人をランダムに選択することによって得られ、それぞれが選択される可能性が等しくなります。
それどころか、判断的サンプリングは非ランダム プロセスです。ここでは、母集団に関する利用可能な情報に基づいてサンプルが選択されます。
システマティックサンプリングとは、集団から一定の間隔で個体を選択する方法です。たとえば、12 人の母集団から 4 人のサンプル・サイズを生成するには、開始点が 1 とサンプリング間隔の間でランダムに選択されます。したがって、3人ごとに選択され、4人の個人のサンプルが作成されます。
層別サンプリングでは、個体群は、個人が共有する特性に基づいてサブグループまたは層に分割されます。次に、各サブグループから比例して個人を選択し、分析用の最終サンプルを構成します。
同様に、クラスターサンプリングには、母集団をサブグループまたはクラスターに分割することも含まれます。その後、いくつかのクラスターが評価のためにランダムに選択されます。

サンプリング計画

サンプリングは分析化学の重要なステップであり、研究者が大規模な母集団から代表的なデータを収集できるようにします。一般的なサンプリング方法には、ランダム、判断、体系的、層別、クラスターサンプリングがあります。

ランダムサンプリングは、母集団の各メンバーがサンプルに選択される可能性が均等である方法です。ランダムサンプリングでは、多くの場合、乱数ジェネレーターまたは抽選タイプの方法を使用して、個人をランダムに選択します。たとえば、ポリマーシートの特性を分析する場合、シートを 1 cm x 1 cm の均等なセクションに分割し、乱数表を使用して 10 セクションをランダムに選択して分析することで、ランダムサンプリングを使用できます。これにより、シート全体で偏りのないサンプルが選択されます。ランダムサンプリングは偏りを最小限に抑え、母集団全体を正確に表すサンプルを作成するのに役立ちます。

判断サンプリングは、目的サンプリングまたは選択的サンプリングとも呼ばれ、研究に最も適していると思われる個人またはサンプルを選択するために研究者の判断または専門知識に依存する非確率法です。たとえば、研究者が魚類におけるポリ塩化ビフェニル (PCB) の生体内蓄積を研究しているとします。その場合、研究者は、小さい、または不健康に見えるなどの特定の基準を満たす魚のみを厳選してサンプリングすることがあります。この方法は、規制当局が収集するサンプルを定義するために特定の基準を要求する場合によく使用されます。

体系的サンプリングでは、ランダムに開始点を選んだ後、集団から n 番目の個体を選択します。たとえば、環境研究では、体系的サンプリングを使用して湖からサンプルを収集できます。そのためには、湖をグリッドに分割し、各セクションから一定の間隔でサンプルを採取して、湖全体の空間的カバーを確保します。このアプローチは、水中の酸素分布などの空間的傾向を含む研究に役立ちます。

層別サンプリングでは、研究に関連する特定の特性に基づいて、集団を明確なサブグループまたは層に分割します。次に、集団内での比率に応じて、各層からサンプルをランダムに選択します。たとえば、都市の空気中の粒子状物質を研究する場合、層別サンプリングを使用して、集団を粒子サイズのカテゴリ (例: 細かい、粗い) に分割できます。次に、各粒子サイズグループからサンプルを採取し、全体の汚染レベルに対する寄与を評価します。この方法では、各サブグループ内でより正確な分析が可能になり、サンプリング誤差が減少します。

サンプリングは分析化学における重要なステップであり、研究者は大規模な集団から代表的なデータを収集することができます。一般的なサンプリング方法...

Education

JoVE Core

Analytical Chemistry

分析化学

Unit 1

ユニット1

Method Development and Sampling Techniques

分析法の開発およびサンプリング技術

method-development-and-sampling-techniques

KEY TERMS AND CONCEPTS

主要用語と概念

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

JoVE Core 分析化学 は、複雑な化学原理をアニメーションで視覚化することで、SI 単位から NMR 分光法を含むトピックをよりわかりやすくします。実験を撮影した実写動画では、これらの概念が世界中の研究所でどのように応用されているかを取り上げています。

analytical chemistry

Choosing Samples for Reliable Results

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