Development and evaluation of the Digit Triplet Test in Swahili language

Background: The development of a Digit Triplet Test in the Swahili language is an essential step towards providing accurate hearing assessment for Swahili-speaking populations. Objectives: This study aimed to develop a Digit Triplet Test in Swahili through a two-part procedure consisting of an optimisation phase and an evaluation phase using normal hearing participants. Method: A total of 34 subjects participated in the study. During the optimisation phase, a psychometric intelligibility function was determined for each recorded digit, allowing for volume adjustments to standardise the threshold across all digits. This resulted in a lower threshold and a steeper psychometric function for both the triplets and the test lists. Using the optimised speech material, four test lists were created, each containing 27 triplets composed of digits between 1 and 9. The finalised material was then evaluated. Results: In the final version, the mean Speech Reception Threshold (SRT) for the participants was -8.9 +/- 0.6 dB Signal-to-Noise Ratio (SNR), and the mean slope was 24.7 +/- 3.5%/dB using triplet scoring. Conclusion: The psychometric function for normal listeners shows a steep slope with little variation between subjects and across test lists. Contribution: The test results are comparable to those of Digit Triplet Tests developed in other languages, indicating the effectiveness and reliability of the Swahili Digit Triplet Test for hearing assessments.