scores permit a more meaningful comparison

The T score is a type of standard score that is based upon the normal curve with a mean of 50 and a standard deviation of 10 for the norm group. Test developers have derived norm tables that allow us to convert a person’s raw score (points earned) to the T score equivalents that would have been obtained if that person had been in the norm group. T scores permit a more meaningful comparison with a norm group than raw scores. Tests for admission to graduate and undergraduate schools (e.g., the Graduate Record Exam) typically use this type of standardized score. The formula frequently used for T score calculation is:

T score=10XSD+(50-10X¯SD)

Where: X = raw score to be converted

X¯ = mean of the group of raw scores

SD = standard deviation of the raw scores

Example: Convert a raw score of 80 to a T score, where X¯ = 75 and SD = 5.

T score=10(80)5+(50-10(75)5)=160+(50-150)=160-100=60

RESEARCH ARTICLE

Source: LoGalbo, A., Sawrie, S., Roth, D. L., Kuzniecky, R., Knowlton, R., Faught, E., & Martin, R. (2005). Verbal memory outcome in patients with normal preoperative verbal memory and left mesial temporal sclerosis. Epilepsy and Behavior, 6 (3), 337–41.

Introduction

LoGalbo et al. (2005) conducted a study to examine the “risk of verbal memory loss in patients with known structural abnormality (i.e., left mesial temporal sclerosis by MRI) and normal preoperative verbal memory performance who undergo left ATL [anterior temporal lobectomy]” (LoGalbo et al., 2005, p. 337). The researchers found that the “patients exhibiting normal presurgical verbal memory are at risk for verbal memory declines following ATL. These results suggest that functional integrity of the left mesial temporal lobe may play an important role in the verbal memory outcome in this patient group” (LoGalbo et al., 2005, p. 337). However, the researchers do recognize the limitations of their study and note that the small sample size restricts the generalization of the study findings.

Relevant Study Results

“Seventeen patients with left temporal epilepsy, MRI-based exclusive left MTS [mesial temporal sclerosis], and normal preoperative verbal memory were identified” (LoGalbo et al., 2005, p. 337). MTS is a structural abnormality in the brain. “The patients selected for the study were considered to have ‘normal’ preoperative verbal memory, defined as having preoperative performance across the learning (Acquisition) and long delayed free recall (Retrieval) portions of the California Verbal Learning Test (CVLT) of at least a T score above 40 (> 16%ile). The CVLT Acquisition score is the total number of words recalled across the five learning trials. The CVLT Retrieval score is defined as total number of words freely recalled after a 20-min delay. Both of these variables have been extensively employed as markers of verbal memory outcome following ATL [anterior temporal lobectomy] in several studies” (LoGalbo et al., 2005, p. 339). Clinical characteristics of these patients are summarized in Table 2, and average CVLT Acquisition and Retrieval T scores are presented in Table 3.

“The average drop in CVLT Acquisition T scores was 6.9, representing a decline of 15% from baseline performance. The average drop in CVLT Retrieval T scores was 9.6, representing a decline on average of 20% from baseline score” (LoGalbo et al., 2005, p. 340).

TABLE 2 CVLT Acquisition and Retrieval T Scores for each Patient