Presentation on theme: "Basic Issues in Measurements P M V Subbarao Professor Mechanical Engineering Department How to generate reliable Numbers?????"— Presentation transcript:
Basic Issues in Measurements P M V Subbarao Professor Mechanical Engineering Department How to generate reliable Numbers?????
The Ultimate Truth of Measurement and Numbers in Engineering & Science It is impossible to measure all most all except two quantities. How to obtain a numerical value? Managers can measure the required attributes more easily than the Engineers and Scientists. The first : Counting. A basis for technical management. The Second: Physical Length.
A Generalized Instrument
Measure: The verb means "to ascertain the measurements of" Measurement: The figure, extent, or amount obtained by measuring" Definition of Measurement
The Measurement Measurement is the process observing and recording the observations that are collected as part of a research effort. There are two major issues to be considered. First, one has to understand the fundamental ideas involved in measuring. These are called as Measurement Concepts. Two of major measurement concepts (Levels & Reliability). Levels of Measurement: There are four major levels of measurement: Nominal, Ordinal, Interval and Ratio. The distinction between real value and nominal value occurs in many fields. From a philosophical viewpoint, nominal value represents an accepted condition which is a goal or an approximation as opposed to the real value, which always is actually present. Often a "nominal" value is "de facto" rather than an exact, typical, or average measurement. Sometimes the word "nominal" is also used in engineering contexts as a synonym for "normal" or "expected"; for example, The rotor resistances on all the other operating wheels are nominal.  
Nominal Value in Engineering For dimensional lumber in North America, a "two by four" is not 2 inches by 4 inches, but rather between 1⅜ and 1⅝ inches thick and between 3⅜ and 3⅝ inches wide, sized to the equivalent rough hewn piece of softwood for nominal structural design purposes. The ⅛-inch tolerances absorb the natural variation and cannot be reduced without risk. Mains electricity is nominally 230 V in the European Union, but is allowed to vary ±10%. A machine is designed to operate at some particular condition, often stated on the device's nameplate. For example, a pump is designed to deliver its nominal pressure and flow while operating at its nominal speed and power.
Ordinal Level of Measurement Rank-ordering data simply puts the data on an ordinal scale. Ordinal measurements describe order, but not relative size or degree of difference between the items measured. The numbers assigned to objects or events represent the rank order (1st, 2nd, 3rd, etc.) of the entities assessed. A Likert Scale is a type of ordinal scale. Uses names with an order such as: "bad", "medium", and "good"; or "very satisfied", "satisfied", "neutral", "unsatisfied", "very unsatisfied."
The Second Major Concept Reliability of measurement: Consideration of true score theory and a variety of reliability estimators. True Score Theory is a theory about that it is not proven: It is postulated as a model of how the world operates. Essentially, true score theory means that every measurement is an additive composite of two components. True ability (or the true level) of the respondent on that measure; and random error. We don't observe what's on the right side of the equation (only God knows what those values are!).
The Second Issue in Measurement Basic understanding of different types of measures: Four broad categories of measurements: Survey includes the design and implementation of interviews and questionnaires. Scaling involves consideration of the major methods of developing and implementing a scale. Qualitative provides an overview of the broad range of non-numerical measures. Quantitative presents a variety of measurement methods that use/generate numerical measures