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Related Concept Videos

Systematic Error: Methodological and Sampling Errors01:15

Systematic Error: Methodological and Sampling Errors

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In the case of systematic errors, the sources can be identified, and the errors can be subsequently minimized by addressing these sources. According to the source, systematic errors can be divided into sampling, instrumental, methodological, and personal errors.
Sampling errors originate from improper sampling methods or the wrong sample population. These errors can be minimized by refining the sampling strategy. Defective instruments or faulty calibrations are the sources of instrumental...
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In statistics, several tools are used to interpret the data. Measures of central tendency represent the characteristics of the data, such as mean, median, and mode. Additionally, measures of variance like standard deviation and range are used to find the spread of data from the mean. Relative standing measures the distance between data locations. Commonly used measures of relative standings are percentile, z score, and quartiles.
Percentiles are a type of fractile that partition data into...
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Data are individual items of information obtained from a population or sample. Data may be classified as qualitative (categorical), quantitative continuous, or quantitative discrete. Because it is not practical to measure the entire population in a study, researchers use samples to represent the population. A random sample is a representative group from the population chosen by using a method that gives each individual in the population an equal chance of being included in the sample. Random...
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Random and Systematic Errors01:20

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Scientists always try their best to record measurements with the utmost accuracy and precision. However, sometimes errors do occur. These errors can be random or systematic. Random errors are observed due to the inconsistency or fluctuation in the measurement process, or variations in the quantity itself that is being measured. Such errors fluctuate from being greater than or less than the true value in repeated measurements. Consider a scientist measuring the length of an earthworm using a...
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Systematic Sampling Method01:17

Systematic Sampling Method

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Sampling is a technique to select a portion (or subset) of the larger population and study that portion (the sample) to gain information about the population. Data are the result of sampling from a population. The sampling method ensures that samples are drawn without bias and accurately represent the population. Because measuring the entire population in a study is not practical, researchers use samples to represent the population of interest.
Systematic sampling is one of the simplest methods...
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Propagation of Uncertainty from Systematic Error01:10

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The atomic mass of an element varies due to the relative ratio of its isotopes. A sample's relative proportion of oxygen isotopes influences its average atomic mass. For instance, if we were to measure the atomic mass of oxygen from a sample, the mass would be a weighted average of the isotopic masses of oxygen in that sample. Since a single sample is not likely to perfectly reflect the true atomic mass of oxygen for all the molecules of oxygen on Earth, the mass we obtain from this...
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Author Spotlight: Demonstrating Systematic Endobronchial Ultrasound to New Endoscopists
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Single screening versus conventional double screening for study selection in systematic reviews: a methodological

Siw Waffenschmidt1, Marco Knelangen2, Wiebke Sieben2

  • 1Institute for Quality and Efficiency in Health Care, Cologne, Germany. siw.waffenschmidt@iqwig.de.

BMC Medical Research Methodology
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Summary

Single screening misses more studies than double screening, impacting systematic review reliability. However, experienced reviewers may use single screening as a shortcut in rapid reviews.

Keywords:
MethodologyStudy selectionSystematic reviews

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Area of Science:

  • Methodology of systematic reviews
  • Evidence-based practice

Background:

  • Systematic reviews require transparent study selection and reliable results.
  • Conventional double-screening is resource-intensive, posing challenges for timely, budget-limited reviews.

Purpose of the Study:

  • To evaluate the equivalence of single screening versus double screening in systematic review processes.
  • To analyze existing evidence on the reliability and efficiency of single screening methods.

Main Methods:

  • Searched Medline, PubMed, and Cochrane Methodology Register up to October 2018.
  • Included evaluations comparing single and double screening, summarizing data narratively.

Main Results:

  • Four evaluations analyzed 23 single screenings; median missed studies were 5% (0-58%).
  • Experienced reviewers missed 3% (0-21%), while less experienced reviewers missed 13% (0-58%).
  • In 7 screenings, findings changed substantially in 3 instances conducted by less experienced reviewers.

Conclusions:

  • Single screening is not equivalent to double screening due to higher missed study rates.
  • Single screening may be a viable shortcut for rapid reviews if performed by experienced reviewers.
  • Further research is needed on factors influencing missed studies in single screening.