What is Classical Test Theory?

Classical Test Theory (CTT) is a framework used in psychology to understand how well tests measure what they're supposed to. Think of it as a way to assess the reliability and validity of psychological tests.

Key Components of Classical Test Theory

CTT focuses on two main aspects:

• True Score: This is the actual score a person would get if the test were perfect, without any errors.
• Observed Score: This is the score that you actually get when you take the test, which can be affected by various factors like anxiety or misunderstanding questions.

The Formula

The relationship between these scores can be summarized in a simple formula:

Observed Score = True Score + Error

Types of Errors in CTT

Errors can occur in various ways, and they can impact the observed score. Here are some common types:

• Systematic Error: This error consistently affects the results in the same direction. For example, if a test is too hard, everyone may score lower than their true ability.
• Random Error: This error varies and can affect the scores unpredictably. For example, a person might score differently on the same test due to mood changes.

Types of Tests in Classical Test Theory

CTT can be applied to different types of psychological tests, including:

• Personality Tests: These tests assess traits like extroversion or conscientiousness.
• Intelligence Tests: These measure cognitive abilities and problem-solving skills.
• Achievement Tests: These evaluate knowledge in specific subjects, like math or reading.

Reliability in Classical Test Theory

Reliability is a crucial concept in CTT. It refers to how consistent the test results are over time. There are several types of reliability:

• Test-Retest Reliability: This means that if you take the same test again after some time, your score should be similar.
• Example: If you take an IQ test this year and the same test next year, a reliable test should show similar results.
• Internal Consistency: This checks if different parts of the test yield similar results.
• Example: If a personality test has multiple questions about extroversion, all those questions should give similar scores.
• Inter-Rater Reliability: This applies when different people score the same test, and their scores should match.
• Example: If two psychologists evaluate the same patient's responses, they should come to similar conclusions.

Validity in Classical Test Theory

Validity refers to how well a test measures what it is supposed to measure. There are different types of validity:

• Content Validity: This checks if the test covers the entire topic it's supposed to measure.
• Example: A math test should include questions on all relevant topics, not just a few.
• Criterion Validity: This assesses how well one test predicts performance on another related test.
• Example: If a new test for anxiety accurately predicts scores on an established anxiety test, it has good criterion validity.
• Construct Validity: This evaluates if the test truly measures the psychological concept it claims to measure.
• Example: If a test is designed to measure depression, it should correlate with other tests measuring the same construct.

Real-Life Examples of Classical Test Theory

Imagine a school using an intelligence test to evaluate students. By applying CTT:

• The school can determine how reliable the test is by checking test-retest reliability.
• They can also see if the test accurately measures intelligence by examining its validity.

In the workplace, employers often use personality tests based on CTT principles to help with hiring decisions. They want to ensure that the tests are reliable and valid to select the best candidates.

Comparison with Item Response Theory

While CTT is widely used, there's another approach called Item Response Theory (IRT) that offers a different perspective. Here’s a quick comparison:

• CTT focuses on overall test scores, while IRT looks at individual item responses.
• CTT assumes that all items are equally difficult, while IRT recognizes that some items are harder than others.
• CTT provides less detailed information compared to IRT, which can offer insights into how each question functions in relation to a test-taker's ability.

Classical Test Theory serves as a fundamental concept in psychology, helping ensure that tests are both reliable and valid. Through understanding its principles, students and practitioners can better appreciate the importance of effective psychological measurement.