Why Counselor's Tests Are Not Reliable

The reason counselor's tests are not reliable is that reliability is a property of scores not tests. This isn't a matter of semantics. Think about it this way.

Give all the students in one school an achievement test. The test items don't change so they appear stable, consistent, and reliable. However, when publishers report reliability values, they calculate the reliability statistics based on scores. Scores vary from one administration to another. If you ever took a test twice and got a different score, you know what I mean. Individuals change from day to day. And we change from year to year. Also, even a representative sample of students for a nation can be different each year.

Everytime we calculate a reliability statistic, the statistic is slightly different.

Reliability values vary with the sample.

Reliability values also vary with the method used for calculation. You can get high reliability values using coefficient alpha with scores from a one-time administration. This method is common in research articles. But you will see different values from the same research team in different samples in the same article.


If we use a split-half method, which usually calculates reliability based on a correlation between two halves of one test, then we can get a reliability value based on one administration. But that's only half a test! Researchers use the Spearman-Brown formula to correct for the shortened half-test problem- but that's just an estimate of what the full test could be.


There's also a test-retest reliability method. Give a test one time, wait awhile- maybe a week or several weeks, then retest. That gives you an estimate of stability. But if you have a good memory, you can score higher on the second test on some tests like intelligence and achievement.


By now you get the point. Any one test can be associated with a lot of reliability values. The problem is not necessarily with counselor tests. The problem can be misunderstanding that tests do not have one reliability value. As with many things in science, there are many variables to consider when answering a question.

Reputable test publishers include reliability values in their test manuals. Counselors, Psychologists, and other test users ought to know about test score reliability.

Learn more assessment and statistical concepts in

Applied Statistics: Concepts for Counselors

AMAZON BOOKS

Connections

My Page    www.suttong.com

My Books   AMAZON     GOOGLE PLAY STORE

FACEBOOK   Geoff W. Sutton

TWITTER  @Geoff.W.Sutton

PINTEREST  www.pinterest.com/GeoffWSutton

Publications (many free downloads)

     

  Academia   Geoff W Sutton   (PhD)

     

  ResearchGate   Geoffrey W Sutton   (PhD)

How to Compare Test Scores

When counselors and psychologists report test scores, they often report one of the scores found in the table below. When several tests are used, it is helpful to know how the scores compare from one test to another.

A good place to begin is to locate the average score-- that's the row where z = 0. Then look at the broad middle range between z = -1 and z = 1. About 68% of people score between z = -1 and z = 1.

Intelligence Tests use Standard Scores abbreviated as SS. These scores take the place of the old IQ score. An average IQ is 100 -- about 68% of people score between 85 and 115.

Here's a table from Appendix B of Applied Statistics: Concepts for Counselors

Each row contains the equivalent score on a different scoring system. For example, a z-score of 1 equals a T score of 60, and a standard score of 115. The score is at the 84^th percentile.

z	T	Standard	Percentile Rank
3	80	145	99.9
2.5	75	138	99.4
2	70	130	97.7
1.5	65	123	93.3
1	60	115	84.1
.5	55	108	69.2
0	50	100	50.0
-.5	45	93	30.8
-1	40	85	15.9
-1.5	35	78	6.7
-2	30	70	2.3
-2.5	25	63	0.6
-3	20	55	0.1

Table Notes

z-scores, M = 0, SD = 1

T-scores, M = 50, SD = 10

SS-Standard Scores, M = 100, SD = 15

PR- Percentile Rank

 Find more practical concepts in Applied Statistics: Concepts for Counselors

An inexpensive reference book for students and counselors

BUY ON AMAZON

Learn more at the book's website  counselorstatistics

Related Posts

Intelligence Tests

Test reliability

Test validity

Understanding the Reliability of Educational and Psychological Tests

Why aren't tests reliable?

The reason tests are not reliable is that reliability is a property of the interpretation of scores not the tests themselves. 

This isn't a matter of semantics.

Think about it this way.

Give all the students in one school an achievement test. The test items don't change so they appear stable, consistent, and reliable. However, when publishers report reliability values, they calculate the reliability statistics based on scores. Scores vary from one administration to another. If you ever took a test twice and got a different score, you know what I mean. Individuals change from day to day. And we change from year to year. Also, even a representative sample of students for a nation can be different each year.


Every time we calculate a reliability statistic, the statistic is slightly different.

Reliability values vary with the sample.

Reliability values vary with the method of calculation.

Reliability values also vary with the method used for calculation. You can get high reliability values using coefficient alpha with scores from a one-time administration. This method is common in research articles. But you will see different values from the same research team in different samples in the same article.


If we use a split-half method, which usually calculates reliability based on a correlation between two halves of one test, then we can get a reliability value based on one administration. But that's only half a test! Researchers use the Spearman-Brown formula to correct for the shortened half-test problem- but that's just an estimate of what the full test could be.


There's also a test-retest reliability method. Give a test one time, wait awhile- maybe a week or several weeks, then retest. That gives you an estimate of stability. But if you have a good memory, you can score higher on the second test on some tests like intelligence and achievement.


By now you get the point. Any one test can be associated with a lot of reliability values. The reliability problem is not just about tests. The problem can be understanding that tests do not have one reliability value. As with many things in science, there are many variables to consider when answering a question.

Reputable test publishers include reliability values in their test manuals. Teachers, Counselors, Psychologists, and other users ought to know about test score reliability.

Learn more assessment and statistical concepts in


Applied Statistics: Concepts for Counselors 

AMAZON BOOKS




Learn more about assessment and statistics at the Applied Statistics website


Learn more about Creating Surveys

Quick Notes on Test Reliability

Reliability is a property of scores not tests.

Reliability may mean stability of scores over time.

Reliability may mean how consistently test questions measure whatever the test measures.

Reliable test scores in one culture do not mean they will be reliable in another culture.

Reliable test scores do not guarantee the score are valid - but reliability places a limit on validity.

Reliability statistical concepts apply to tests, quizzes, polls, surveys...sets of questions yielding numerical scores.



Note: This is a re-posting of a post to this new blog. 

Links to Connections

My Page    www.suttong.com

  

My Books  AMAZON          and             GOOGLE STORE

 

FOLLOW   FACEBOOK   Geoff W. Sutton   TWITTER  @Geoff.W.Sutton

 

PINTEREST  www.pinterest.com/GeoffWSutton

 

Articles: Academia   Geoff W Sutton   ResearchGate   Geoffrey W Sutton