Tests of Dyslexia (TOD™) FAQs
1. What is the TOD?
The TOD is a comprehensive battery of tests and resources designed to help identify and plan interventions for individuals of all ages with dyslexia.
The TOD has three batteries: the TOD-Screener, three tests that can be administered to groups of students or to individuals, available in a paper or digital format; the TOD-Early, designed for the early identification of students in Grades K–2 (5 years, 0 months–9 years, 3 months); and the TOD-Comprehensive, designed for examinees from Grade 1 to adulthood (6 years, 0 months–89 years, 11 months).
The TOD includes
- indexes designed to indicate the risk and probability of dyslexia;
- composites and tests that measure reading skills (untimed and timed), spelling, specific linguistic risk factors (phonological awareness, orthographic processing, rapid automatized naming, and working memory), and vocabulary and reasoning abilities;
- self, parent, and teacher rating scales designed to capture qualitative indicators of dyslexia, such as a family history of reading problems and early difficulties with speech and language; and
- the Dyslexia Interventions and Recommendations guide to help examiners develop IEPs and targeted intervention plans to address specific skill weaknesses.
2. What sets the TOD apart from other reading assessments?
First, the TOD covers a wide age range and includes the major components that are needed for a comprehensive dyslexia assessment. There is no need to cobble together results from different tests with different norm groups.
Second, the TOD includes the reading and linguistic abilities that are most relevant to the diagnosis of dyslexia. The TOD includes measures of word recognition (untimed and timed), phonics knowledge, reading fluency, and comprehension efficiency (the ability to comprehend text under time pressure). The TOD also includes linguistic risk factors (e.g., phonological awareness, rapid automatized naming) that can help you determine the factors that are affecting reading development.
Third, the TOD includes measures of vocabulary and reasoning to help you determine if the reading problem is specific and/or unexpected in relation to abilities that do not require reading.
Fourth, the TOD includes rating scales to help standardize the process of collecting information from parents, teachers, or individuals being assessed.
Fifth, the TOD includes a guide to interventions to help you develop an instructional plan.
3. Who can purchase the TOD?
Professional standards in testing are presented in the Standards for Educational and Psychological Testing published by the American Educational Research Association (AERA), American Psychological Association (APA), and the National Council on Measurement in Education (NCME). Examiners should use only those tests for which they have the appropriate training and expertise.
Test publishers provide qualification guidelines to help determine who may purchase their tests. WPS has the following guidelines:
All the TOD components can be purchased by educators, psychologists, and related professionals who serve students who may have dyslexia. These are Level B tests, so examiners must have a bachelor’s degree in psychology or a related discipline (e.g., school counselors, speech and language pathologists, social workers, special education teachers, medical professionals) and training and instruction in administration and interpretation of standardized tests.
4. Who can use the TOD?
The components of the TOD can be used by a variety of clinicians and educators. For example, a classroom teacher may administer the TOD-Screener and complete the Teacher Rating Scale.
Reading specialists, educational diagnosticians, psychologists, and speech–language pathologists are best suited to administer the TOD-Early or the TOD-Comprehensive due to their advanced coursework and experience with standardized tests. Teachers trained to administer the test and supervised by professionals with advanced training with standardized assessments may also administer the TOD-E or TOD-C.
Interpreting test results requires a higher level of skill. For that reason, while a broader range of individuals can administer the test, interpreting results requires a knowledge of dyslexia and formal training in test administration, scoring, and interpretation.
5. What is the reliability/validity of the TOD?
The answer to this question is complicated and requires some context. Reliability and validity evidence occurs over time and from multiple studies and methodologies. It cannot be defined by single scores. Expert recommendations for interpreting reliability and validity estimates are produced by statistical equations.
Reliability estimates are assumed to reflect the percentage of systematic variance in a test (vs. error) and can be calculated using statistical equations. The two most common reliability formulae are Cronbach’s Alpha and Spearman-Brown. Both yield coefficients designed to estimate the magnitude of the linear relationship between two variables, perhaps two versions of the same test. The most common correlational statistics assess relationships between either two interval-level variables (i.e., the Pearson Product Moment Correlation Coefficient) or two ordinal variables (i.e., Spearman’s Rho). Authors of tests and measurement texts (e.g., Sattler, 2018) provide criteria for interpreting these reliability coefficients (after Murphy & Davidshofer, 2005).
Values above .90 are considered high/excellent; .80 to .89, moderately high or good; .70 to .79, moderate or fair; .60 to .69 low or poor; and .00 to .59, very low. Reliability coefficients set the limits on validity; for example, the square root of a reliability coefficient of a test defines the maximum predictive validity of that instrument.
Validity is traditionally defined as the extent to which a test does what it was designed to do and, like reliability, is typically operationalized using correlation coefficients. Understanding the conceptual nature of “validity” is more complicated than reliability. Tests are valid for particular purposes. For example, validity coefficients address the extent to which a test assesses the construct it was created to address.
Thus, construct validity is determined in part by how strong the correlation coefficient is between the test in question, say a newly developed test, and an established instrument that measures similar skills. In addition, validity data can inform prediction, i.e., how well a test predicts some criterion of interest. As an example, intelligence tests are often used to predict academic achievement. Across many studies reported in test manuals and in the general literature, these validity coefficients typically range from about .40 to .70, indicating that the percentage of the variance accounted for in achievement by intelligence ranges from about 16% to 49%.
Reliabilities for the TOD tests and composites are typically good (i.e., greater than .80), as reported in the TOD Manual. Similarly, validity estimates are good also. For example, the TOD-C Dyslexia Diagnostic Index is a strong predictor of the probability of dyslexia.
In summary, data generally support the reliability of the TOD indexes, composites, and tests and the validity of these scores for their intended purposes. Consequently, examiners can have confidence in the TOD scores.
References:
Murphy, K. R., & Davidshofer, C. O. (2005). Psychological testing: Principles and applications (6th ed). Pearson Education.
Sattler, J. M. (2018). Assessment of children: Cognitive foundations and applications (6th ed). Jerome M. Sattler Publisher.