The Developmental Profile (DP-3) is an assessment designed to detect developmental delays or disabilities. It helps address areas in which a child lacks the developmental ability needed to grow normally. The DP-3 covers five critical domains of development including adaptive behavior, physical, social-emotional, communication, and cognitive growth.

Standard Error of Measurement

The Standard Error of Measurement (SEM) is a measure of reliability used to estimate the amount of error in a test score. It produces a reasonable approximation of the amount in which an observed score is different from a true score in a test with no error.

SEM values have the most practicality when they are used to calculate the confidence interval of an individual. Confidence intervals represent where an individual’s true score lies. The 95% confidence level is used as the standard in psychology and is used to evaluate the DP-3.

A confidence range of plus or minus ten points on all five domains is recommended for children aged zero to five years, eleven months, while a range of nine points higher or lower is used for ages six to twelve years, eleven months.

For a child of four years, five months who produces a score of 90 on any of the five scales has a 95% probability that their true score is between 80 and 100. Exact confidence intervals are available at 90% and 95% for users who would like to know.

The Parent/Caregiver Checklist and the Interview Form show the same correlations of good to excellent, showing a strong reliability using the Standard Error of Measurement.


The Standard Error of Measurement proves the DP-3’s reliability based on the consistency of the scores and uniformity across the Parent/Caregiver Checklist and Interview Form. The reliability of the DP-3 is critical for users who need to know they can depend on the assessment to be error-free.

The other two types of reliability are based on internal consistency and test-retest data. Internal consistency shows how well the items on each of the five scales reflect the underlying construct, defined by the five domains the DP-3 measures.

To measure internal consistency, the split-half method is used. This method alternates consecutive items on each scale, creating two halves. The Pearson correlation that results from the two halves is adjusted using the Spearman-Brown formula, estimating the reliability of the entire scale.

For each age represented, the DP-3 internal consistency results are all above .80, meaning that the correlations are good, if not excellent. Many of the correlations are .90 or more, indicating a strong reliability in the DP-3.

Test-retest reliability involved administering the DP-3 assessment to the same parents on two different occasions and comparing the results. Using sixty-six participants from various ages, education levels, ethnicities, and genders, and an average of two weeks between test scenarios, the test-retest method indicates .81 to .92 for all five scales.

This demonstrates the reliability of the assessment based on the test-retest principle across all ages and demographics.

The reliability of the DP-3 is essential for test users to evaluate a child’s developmental progress, detect delays, and implement intervention programs or suggest intervention activities. For more information on the DP-3, visit WPS Publish.