Reliability and Validity

Topics: Psychometrics, Validity, Reliability Pages: 54 (5464 words) Published: July 23, 2012
C.4.4 Item and Test Analysis: Determination of Test Quality
Kanupriya Katyal, Dr. Jagrook Dawra

This module deals with defining and determining quality of test instruments and test items. Tests as an instrument for evaluation need to be accurate, objective, practical and reliable. Further they should be able to discriminate between good and bad performers and have a uniform difficulty level. This module explains each of these terms and describes how they can be measured. Module specifically tou ched on six measures of test quality, objectivity, practicability, reliability, validity, difficulty level and discrimination index. It also talks about mathematical measures like mean, median, mode, standard deviation and correlation that help in measuring test quality.


To enable the reader to define the quality of a test and measure it. a.

To understand the concepts of reliability and validity in a test.


To understand the various measurements used in defining quality like mean, median, mode, standard deviation & correlation

A test needs to evaluate and measure the performance of the candidate, department or an institution. Measurement is purely quantitative and when an individual‟s judgment is added it becomes evaluation. A test should measure what it intended to measure, with considerable accuracy and at the same time it should be able to discriminate between students of varied abilities. Subjective judgment leads to inaccuracy and errors. These errors are the standard errors of mea surements. Hence, these need to be identified and eliminated.

There are several valid reasons for analyzing questions and tests that students have completed and that have already been graded. Some of the reasons include the following: 

Identify content that has not been adequately covered and should be re-taught,

Provide feedback to students,

Determine if any items need to be revised in the event they are to be used again or become part of an item file or bank,

Identify items that may not have functioned as they were intended, 1

Direct the teacher's attention to individual student weaknesses.

Validity and reliability are the overarching principles that govern test design. Validity is the extent to which a test measures what it intends to measure. Reliability is the extent to which the test scores are consistent. Reliability is a property of the test as a measuring instrument. Other measures like objectivity, practicability, difficulty level and discrimination index are also some measures of test quality and have been discussed in the subsequent sections.

Understanding Test Item and Test Quality
There are various forms of assessment techniques available to examiner. They range from assessing students using a fixed-response multiple choice test or an open-response short answer, long answer or essay type of exam. These exams serve a variety of purposes. The results may be used to access a student‟s strengths and weaknesses or plan further instructional activity. They may be used for selection, placement or for certification. They may be used as tools for appraisals. Regardless of the objective of assessment, all assessments need to possess certain characteristics and need to have a certain degree of quality. A test is said to be of good quality if it satisfies the following criteriai: 1.

Objectivity (justice): Objectivity is said to be ensured when the paper setter is given a design/ method to follow. Objectivity of the „darts‟ exercise would depend upon how well is the task defined to the players. A test with good objectivity would define number of attempts, distance from where to aim, etc.

For example, teachers at several levels of education assess students‟ overall learning by giving them projects. Often, students are not told anything about the scope of the wo rk. They are also unaware of what distinguishes a good project from a bad project...
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