Good day everyone! I am Merele P. Plasencia. I will be discussing the continuation topic for Chapter 7
which is the Reliability.
SLIDE 3 What is reliability? The reliability of a measuring instrument is the degree of consistency with
which it measures whatever it is measuring. This quality is essential in any kind of measurement. Reliability
can be estimated by comparing different versions of the same measurement.
SLIDE 4 There are 2 kinds of error, the random error and the systematic error. Random error is a result of
pure chance and the root of reliability problems. It isn't necessarily a mistake, but rather a natural part of
measurement. Random errors of measurement may inflate or depress any subject’s score in an
unpredictable manner.
On the other hand systematic error is predictably inflate or depress scores of identifiable groups. It is the
source of validity issues. In research, it is typically more difficult than random errors.
SLIDE 7 Before moving on the next topic, remember the importance of determining the difference between
the random error and systematic error when you are doing your research. To decide whether you are
dealing with reliability or validity, you determine whether you are considering random errors or systematic
errors. Recognizing the kind of error allows you to mitigate their effects and record accurate and precise
measurements. Gone unnoticed, these errors can lead to research biases like omitted variable bias or
information bias.
SLIDE 9 Now let’s discuss the 3 sources of random error. First is The individual being measured may be a
source of error. Next is The administration of the measuring instrument may introduce error. And lastly, The
instrument may be a source of error. We will this 3 sources pf random error one by one.
SLIDE 10 The first source of random error is The individual being measured may be a source of error. In
this source of error, Individuals' encouragement, curiosity, level of tiredness, physical well- being,
anxiousness, and other psychological and emotional factors all have an impact on test results. Because
these factors change at random from one measurement to the next, one's scores change or become
inconsistent.
SLIDE 11 The second source of random error is The administration of the measuring instrument may
introduce error. A novice may deviate from standardized procedures when administering a test. Light,
temperature, air circulation, period of the day, and the involvement of distractions can all have an impact on
test performance. Subjectivity and ambiguous scoring instructions depress consistency, whereas objectivity
and accurate scoring procedures boost it.
SLIDE 12 The third and last source of random error is The instrument may be a source of error. Brevity or
shortness of time of a test is a key cause of unreliability. An unstable score is produced by a limited
selection of behavior. For instance, if an exam is given to evaluate how well students know the capitals of
the 50 states, but only five questions are asked, a student who knows only ten capitals may get all five
questions completely right, whereas a student who knows forty may get none. In a short test, luck plays a
larger role compared to a long test.
SLIDE 13 Let’s move on the Equation for Equality. Here are the important terms we need to remember.
First is the observed score, When you give a student a test, you get a score, which is known as the
observed score. If you tested this student again using the same tool, you would most likely not have
obtained the same observed score due to the influence of error of measurement. Let us assume that test
scores have an error component implying that a hypothetical error-free score for an individual would be
achieved if the measurement were perfectly accurate. This error-free value is referred to as the individual's
true score.
In other words, the observed score is the actual exam score, while the true score is the person's true ability.
Error of measurement may be caused by any one, or a combination, of a number of factors associated with
variations within the examinee from time to time or with the test and its administration.
SLIDE 14 The idea of error component and true component in a single test score may be represented
mathematically by Formula shown in the slide. So the the observe score is represented as x, the true score
is the t while e is the error-of-measurement component.
SLIDE 16 We can now conclude that every test score consists of two components: the true score plus
some error of measurement. The true score component may be defined as the score an individual would
obtain under conditions in which a perfect measuring device is used.
Next is that The error-of-measurement component can be either positive or negative. If it is positive, the
individual’s true score will be overestimated by the observed score; if it is negative, the person’s true score
will be underestimated. Because researchers assume that an error of measurement is just as likely to be
positive as it is to be negative, they can conclude that the sum of the errors and the mean of the errors
would both be 0 if the same measuring instrument or an equivalent form of the instrument were
administered an infinite number of times to a subject
Lastly, Under these conditions, the true component would be defined as the individual’s mean score on an
infinite number of measurements. The true score is a theoretical concept because an infinite number of
administrations of a test to the same subject is not feasible.