Sampling Methods Overview
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Questions and Answers

What is the primary characteristic of systematic sampling?

  • Samples are taken from homogenous populations only.
  • Samples are selected based on the researcher's judgment.
  • Samples must be collected continuously without gaps.
  • Samples are taken at random intervals. (correct)

    • What does stratified sampling involve?

  • Selecting entire subgroups randomly.
  • Collecting samples from heterogeneous populations only.
  • Randomly choosing individuals without any subgroup consideration.
  • Dividing the population into subgroups and selecting from each. (correct)

    • Which sampling method combines multiple grab samples into one before analysis?

  • Grab sampling
  • In situ sampling
  • Judgmental sampling
  • Composite sampling (correct)

    • What is one disadvantage of composite sampling?

    <p>Individual characteristics of samples may be lost.</p> Signup and view all the answers

    In what situation is grab sampling most appropriate?

    <p>When needing a snapshot of a homogenous population.</p> Signup and view all the answers

    How does in situ sampling differ from other sampling methods?

    <p>It involves collecting samples directly from the environment.</p> Signup and view all the answers

    What is the advantage of using systematic grab sampling over simple grab sampling in a heterogeneous population?

    <p>It helps to characterize how properties change over time or space.</p> Signup and view all the answers

    Which of the following is NOT a common method for obtaining samples?

    <p>Randomized grouping</p> Signup and view all the answers

    What is a major disadvantage of grab samples and composite samples?

    <p>They cannot be used for continuous monitoring of changes in the target population.</p> Signup and view all the answers

    What is the main purpose of in situ sampling?

    <p>To monitor a target population continuously without sampling individual specimens.</p> Signup and view all the answers

    Which step is NOT involved in sampling bulk material?

    <p>Performing destructive testing on individual specimens.</p> Signup and view all the answers

    What is the key characteristic of a homogeneous target population during sampling?

    <p>Individual samples do not need to consider location.</p> Signup and view all the answers

    What is a significant error source in sample collection prior to trace analysis?

    <p>Contamination of sampling tools and vessels.</p> Signup and view all the answers

    Why is it important to select multiple individual samples from different locations in a heterogeneous population?

    <p>To correctly represent the total population's properties.</p> Signup and view all the answers

    Why is it important to minimize adsorption of analytes during sample collection?

    <p>It improves the accuracy of the measurements taken post-sampling.</p> Signup and view all the answers

    Which of the following methods ensures that every member of the population has an equal chance of selection?

    <p>Simple random sampling</p> Signup and view all the answers

    Which material is recommended for dissecting human and animal tissues during sample collection?

    <p>Tools made from quartz glass rinsed with ultrapure acids.</p> Signup and view all the answers

    What is a common issue that arises when sampling is done in a haphazard manner?

    <p>There is a higher chance of obtaining a biased sample.</p> Signup and view all the answers

    What factor must be considered regarding the time of sampling?

    <p>The season in which the sampling occurs.</p> Signup and view all the answers

    What is described by the term 'sampling error'?

    <p>The difference in characteristics of the sample and the population.</p> Signup and view all the answers

    What is the correct procedure for reducing a gross sample in laboratory sampling?

    <p>Select a smaller portion that best represents the original sample.</p> Signup and view all the answers

    During which type of sampling do researchers rely on their personal judgment to select units?

    <p>Non-probability sampling</p> Signup and view all the answers

    Which sampling method typically gives a more accurate representation of a complex system such as a lake affected by pollution?

    <p>Composite sampling</p> Signup and view all the answers

    In sampling techniques, what does in situ sampling typically refer to?

    <p>Samples collected directly from the population without prior disturbance.</p> Signup and view all the answers

    Study Notes

    Sampling Methods

    • Systematic Sampling - select first sample randomly and then take samples at intervals, this could be every 5th, 10th, or even every 5 minutes, 10 minutes
    • Stratified Sampling - divide the population into subgroups and then select samples from each subgroup
    • Cluster Sampling - divide the population into clusters (each cluster should have similar characteristics to the whole populations) and then randomly select entire clusters

    Types of Samples

    • Grab Sample - take a portion of the population at a specific time and location, this provides a snapshot of the population
    • Composite Sample - combine several grab samples, used to determine the population's average composition over time or space
    • In Situ Sample - uses an analytical sensor to continuously monitor a target population without needing to remove samples

    Error Sources Prior to Total Element Determination

    • Contamination - take care to avoid contamination of all tools and vessels, especially with samples that have very low trace element levels (like blood, urine, or seawater) . The time of sampling can be very important especially for body fluids or fresh waters (rivers or lakes)
    • Time of sampling - consider the time of day.

    Sampling Methods (Techniques)

    • Probability (Random) Sampling - every member of the population has the same chance of being selected, this method minimizes bias
    • Non-Probability Sampling - use personal judgment to select samples,
    • Simple Random Sampling - every sample has an equal chance of being selected

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    Description

    Test your understanding of various sampling methods with this quiz. It covers systematic, stratified, and cluster sampling techniques, along with types of samples such as grab, composite, and in situ samples. Additionally, it addresses potential errors from contamination in sampling processes.

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