6702_reliability & validity

8/10/2019 6702_Reliability & Validity

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RELIABILITY & VALIDITY

After assigning numerals to objects or events according to rules, an investigatorfaces two major problems viz. reliability and validity. He has devised hismeasurement game and has administered the measuring instrument to a groupof subjects. He has a set of numbers, the end product of the measurementgame. He must now ask and answer the questions: hat is the reliability of themeasuring instrument! hat is its validity! "hese two aspects viz., reliabilityand validity are of prime importance to a researcher.

Reliability:

#ynonyms for reliability are: dependability, stability, consistency, predictability $accuracy. A reliable man, for instance, is a man whose behavior is consistentdependable, and predictable%what he will do tomorrow and ne&t week will beconsistent with what he does today and what he has done last week. "hus, he isa reliable man. 'n the other hand, an unreliable man is one whose behavior ismuch more variable. He is unpredictably variable. #ometimes he does this,sometimes that. He lacks stability. e say he is inconsistent.

Reliability Defined:

(t is possible to approach the definition of reliability in three ways. 'ne approachis epitomized by the question: (f we measure the same set of objects again andagain with the same or comparable measuring instrument, will we get the sameor similar results! "his question implies a definition of reliability in stability,dependability $ predictability terms.

A second approach is epitomized by the question: Are the measures obtainedfrom a measuring instrument the )true* measures of the property measured!

"his is an accuracy definition. +ompared to the first definition, it is furtherremoved from common sense and intution, but it is also more fundamental."hese two approaches or definitions can be summarized in the words stabilityand accuracy.

"here is a third approach to the definition of reliability, an approach that not onlyhelps us better define and solve both theoretical and practical problems but alsoimplies other approaches and definitions. e can inquire: how much error ofmeasurement is there in a measuring instruments! ecall that there are twogeneral types of variance: systematic and random. #ystematic variance leans inone direction: scores tend to be all positive or all negative or all high or all low.

-rror in this case is constant or biased. ut random or error variance is self%compensating: scores tend now to lean this way, now that way. -rrors ofmeasurement are random errors. "hey are the sum or product of a number ofcauses: the ordinary random or chance elements present in all measures due tounknown causes, temporary or momentary fatigue, fortuitous conditions at aparticular time that temporarily affect the object measured or the measuringinstrument, fluctuations of memory or mood, and other factors that are temporaryand shifting. "o the e&tent that errors of measurement are present in ameasuring instrument, to this e&tent the instrument is unreliable. (n other words,reliability can be defined as the relative absence of errors of measurement in ameasuring instrument.


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"he more widely accepted approach/e&planation of reliability is through error: themore error, the greater the unreliability0 the less error, the greater the reliability.1ractically speaking, this means that if we can estimate the error variance of ameasure we can also estimate the measure2 s reliability. "his brings us to twoequivalent definitions of reliability:

3. eliability is the proportion of the )true* variance to the total obtained

variance of the data yielded by a measuring instrument.4. eliability is the proportion of error variance to the total obtained variance

yielded by a measuring instrument subtracted from one.

(t is easier t write these definitions in equation form:

V

Rtt = --------------- .. (1)VtVe

Rtt = 1 - ----------- .. (2)Vt

And Vt= V Ve .... (!)

"#e$e% $tt i t#e $eliability 'effi'ient

V i t$e *a$ian'eVt i btained *a$ian'eVe i e$$$ *a$ian'e

5-q. 3 is theoretical and cannot be used for calculation unless there is anassumption that the true variance is equal to the population variance. -q 4can be used both to conceptualize the idea of reliability and to estimate thereliability of an instrument. An alternate equation to -q. 4

Vt+ V Rtt = ----------------------- . (,)

Vt

"his alternate definition of reliability will be useful in helping us to understandwhat reliability is.

T#e Inte$$etatin f t#e Reliability effi'ient:

(f r, the coefficient of correlation, is squared, it becomes a coefficient ofdetermination, that is, it gives us the proportion or percentage of the varianceshared by two variables. (f r 6 .78, then the two variables share 9.78468.;3percent of the total variance of the two variables in common. +oefficient ofdetermination has a wider use in regression anylysis 94. #imilarly, thereliability coefficient is also a coefficient of determination. "heoretically, it tellshow much variance of the total variance of a measured variable is )true*variance. (f we had the )true* scores and could correlate them with the scoresof the measured varies and square the resulting coefficient of correlation, wewould obtain the reliability coefficient.


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T#e Vale f Reliability:

"o be interpretable, a test must be reliable.


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find out indirect means to measure these psychological properties oreconomic phenomenon. "hese measures are so indirect that the validity ofthe measurement and its product is often doubtful. "hus, we may summarizethat validity is a descriptive term used of a measure that accurately reflectsthe concept that it is intended to measure. =or e&ample, your intelligencequotient would seem a more valid measure of your intelligence than would thenumber of hours you spend in the library. (t is important to realize that theultimate validity of a measure can never be proven. ?et we may agree to its

relative validity. esearchers distinguish between three types of validity viz.,content, criterion $ construct validity.

ntent Validity:(i) +ontent validity is the representativeness or sampling adequacy or

the content. @alidation is guided by the question: (s the substanceor content of this measure representative of the content or theuniverse of content of the property being measured! (n empiricalresearch content validity refers to the e&tent to which a measuringinstrument provides adequate coverage of the topic under study.=or e&ample, if the instrument contains a representative sample of

the universe the content validity is good.(ii) $ite$in Related Validity:+riterion%related validity is studied by comparing test or scale scores with oneor more e&ternal variables, or criteria, known or believed to measure theattribute under study. hen one predicts success or failure of students fromacademic aptitude measures, one is concerned with criterion%related validity.How well does the test 9or tests predict to graduation or to grade%pointaverage! 'ne does not care so much what the test measures as one caresfor its predictive ability. (n fact, in criterion%related validation, which is oftenpractical and applied research, the basic interest is usually more in thecriterion, some practical outcome, than in the predictors. "he higher the

correlation between a measure or measures of academic aptitude and thecriterion, say grade%average, the better the validity. (n empirical researchwhere relationship between variable are studied criterion related validity mayrelate to the predictive efficiency of the model and the variables used. (t isstudied by comparing actual/real observations with the predicted one usinge&ternal variables. "aking an e&ample from the economy one may studyinvestment potentiality with the help of either composition of income group ormarginal prosperity to save 91# of a group of people. A question ariseswhich of the two e&planatory variables could predict investment potentialityaccurately. (n such cases we address the problem of criterion%relatedvalidity.


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(iii) nt$'t Validity:#cientifically speaking, construct is one of the most significant advances ofmodern measurement theory and practice. (t is a significant advancebecause it unites psychometric notions with theoretical notions.A researchergenerally starts with the constructs or variables entering into the relations. Hehas discovered, say a positive correlation between sale volume andadvertising e&penditure. "he researcher wants to know why this relationshipe&ists, what is behind it. "o learn why, he must know the meaning of the

constructs entering the relation. "aking another e&ample we may considerthat price may not play a significant role in the demand for a high pricedconsumer durable rather attitude of the people belonging to the high incomegroup towards the product could be the determining factor of the saiddemand. "herefore, a researcher has to ask a question himself here, thatwhich variable price or attribute could e&plain the variation in demand of theabove mentioned good. He also tries to articulate why such relationshipcould e&ist. "hus, he goes into the meaning of the relationship which is aconstruct validity problem. (n otherwords proper articulation with valid logicare associated with construct validity.'ne can see that construct validationand empirical scientific inquiry are closely allied. (t is not simply a question of

validating a test. 'ne must try to validate the theory behind the test and thelogic behind the relationship."he significant point about construct validity,which sets it apart from other types of validity, is its preoccupation with theory,theoretical constructs, logical articulation and scientific empirical inquiryinvolving the testing of hypothesized relations.

/te: 1articipants are required to understand the above three types ofvalidity by taking/articulating several real life e&amples from theeconomy/market.

"hey are advised to go through the relevant chapters on the above concepts

in the following books for a detail study.

Foundation of Behavioral Research by F.N. Kerlinger.

6702_reliability & validity

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