List and explain five factors affecting measurement and evaluation

relatively straightforward multiple-choice items to more complex simulations and portfolio assessments. Knapp noted that some of the recent innovations in computer-based assessments allow for a variety of “glitzy” options, but she cautioned that while these options may be attractive, they may not be the best way to assess the targeted construct. The primary focus in deciding on the assessment method is to consider the knowledge, skill, and/or behavior that the test developer would like to elicit and then to consider the best—and most cost-effective—way to elicit it.

Knapp discussed two decisions to make with regard to constructing test items: the type of stimulus and the response mode. The stimulus is what is presented to the test taker, the task to which he/she is expected to respond. The stimulus can take a number of different forms such as a brief question, a description of a problem to solve, a prompt, a scenario or case study, or a simulation. The stimulus may be presented orally, on paper, or using technology, such as a computer.

The response mode is the mechanism by which the test taker responds to the item. Response modes might include choosing from among a set of provided options, providing a brief written answer, providing a longer written answer such as an essay, providing an oral answer, performing a task or demonstrating a skill, or assembling a portfolio of materials. Response modes are typically categorized as “selected response” or “constructed-response,” and constructed-response items are further categorized as “short-answer constructed-response,” “extended-answer constructed-response,” and “performance-based tasks.” Response modes also include behavior checklists, such as those described by Candice Odgers to assess conduct disorders, which may be completed by the test taker or by an observer. The response may be provided orally, on paper, through some type of performance or demonstration, or on a computer.

Knapp explained that choices about the stimulus type and the response mode need to consider the skill to be evaluated, the level of authenticity desired,3 how the assessment results will be used, and practical considerations. If the test is intended to measure knowledge of factual information, a paper-and-pencil test with brief questions and multiple-choice answer options may be all that is needed. If the test is intended to measure more complex skills, such as solving complex, multipart problems, a response mode that requires the examinee to construct an answer is likely to be more useful.

Layered on top of these considerations about the best ways to elicit the targeted skill are practical and technical constraints. Test questions

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3Authenticity refers to how closely the assessment task resembles the real-life situation in which the test taker is required to use the skill being assessed. As described earlier, the level of authenticity desired is an issue that should be addressed as part of a needs analysis.

Factors affecting the accuracy of the Measuring System

The basic components of an accuracy evaluation are the five elements of a measuring system such as:

•             Factors   affecting   the   calibration   sta

•             Factors   affecting   the   work   piece.

•             Factorsngthe inherentaffecticharacteristics of the instrument.

•             Factors   affecting   the   person,   who   car

•             Factors   affecting   the   environment.

1.     Factors affecting the Standard: It may be affected by:

-Coefficient of thermal expansion

-Calibration interval

-Stability with time

-Elastic properties

-Geometric compatibility

2.                 Factors affecting the Work piece: These are: -Cleanliness

-Surface finish, waviness, scratch, surface defects etc., -Hidden geometry

-Elastic properties,-adequate datum on the work piece -Arrangement of supporting work piece 

-Thermal equalization etc.

3.                 Factors affecting the inherent characteristics of Instrument: -Adequate amplification for accuracy objective

-Scale error

-Effect of friction, backlash, hysteresis, zero drift error

-Deformation in handling or use, when heavy work pieces are measured -Calibration errors

-Mechanical parts (slides, guide ways or moving elements) -Repeatability and readability

-Contact geometry for both work piece and standard.

4.     Factors affecting person:

-Training, skill

-Sense of precision appreciation

-Ability to select measuring instruments and standards -Sensible appreciation of measuring cost

-Attitude towards personal accuracy achievements

-Planning measurement techniques for minimum cost, consistent with precision requirements etc.

5.  Factors affecting Environment:

-Temperature, humidity etc.

-Clean surrounding and minimum vibration enhance precision -Adequate illumination

-Temperature equalization between standard, work piece, andinstrument -Thermal expansion effects due to heat radiation from lights

-Heating elements, sunlight and people

-Manual handling may also introduce thermal expansion.

Higher accuracy can be achieved only if, ail the sources of error due to the above five elements in the measuring system are analyzed and steps taken to eliminate them. The above analysis of five basic metrology elements can be composed into the acronym SWIPE, for convenient reference where,

S –STANDARD            W –WORKPIECE I –INSTRUMENT

P –PERSON                  E –ENVIRONMENT

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Mechanical : Metrology and Measurements : Concepts of Measurement : Factors affecting the accuracy of the Measuring System |

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