Impact of Question 8 (Likert Scale) on MMAS-8 Psychometric Properties:

Academic journals indicate that question 8 of the MMAS-8, with its five-point Likert response scale, generally contributes positively to the scale's psychometric properties. Here's a breakdown of its key impacts:

1. Construct Validity and Factor Structure:

• Supports unidimensionality: Studies consistently show that the Likert-scored question 8 aligns with the one-factor structure of the MMAS-8, meaning it contributes to a single index of adherence measurement.
• Contributes to explaining variance: The item's Likert format doesn't disrupt the overall unidimensionality and all items, including question 8, load onto a single factor, explaining a significant portion of the variance in adherence scores.
• May also measure a specific aspect of adherence:While primarily contributing to the overall adherence index, some studies suggest question 8 may also capture a distinct facet related to memory or cognitive barriers, as it's part of a principal component alongside items concerning those factors.

2. Reliability:

• Supports adequate reliability: Studies on the MMAS-8 generally report acceptable internal consistency (e.g., Cronbach's alpha of 0.83), indicating that question 8's inclusion supports the scale's reliability in measuring medication adherence in certain populations.

3. Convergent Validity:

• Enhances sensitivity to adherence variations:Question 8's Likert format provides graded responses, enhancing the scale's ability to detect variations in adherence behavior.
• Correlates with related constructs: Significant correlations exist between MMAS-8 total scores (including question 8) and scales measuring related psychological constructs like the 10-item Drug Attitude Inventory, Form C of the Multidimensional Health Locus of Control scale, and the Hong Psychological Reactance Scale, according to the NIH. This suggests question 8 contributes to the scale's ability to capture psychological and behavioral factors influencing adherence.
• Differentiates adherence levels: The MMAS-8, including question 8, can differentiate adherence levels across various mental disorder diagnosis groups, indicating its helpfulness in capturing nuanced differences in adherence behavior.

4. Sensitivity and Specificity:

• Improved identification of adherence levels: The MMAS-8, with question 8's Likert scale, shows acceptable sensitivity and specificity in identifying low, medium, and high adherence levels (scores <6, 6-7, and 8, respectively).
• Allows for finer distinctions: Question 8's graded responses allow for more nuanced distinctions in adherence challenges, especially those related to memory, which is valuable in populations with cognitive impairments.

5. Challenges with Likert-Type Responses:

• Potential for response biases: The use of a Likert scale introduces potential issues like response biases (e.g., acquiescence or social desirability). However, the MMAS-8's overall psychometric properties remain robust despite this limitation.
• Practicality of the five-point scale: The five-point format of question 8 is considered practical and effective for clinical settings, balancing sensitivity with ease of use.

Specific Considerations for Question 8:

• Standardized scoring: Question 8's Likert responses (0-4) are standardized by dividing by 4 to align with the 0-1 scoring of dichotomous items, ensuring a total MMAS-8 score range of 0-8.
• Relevance in specific populations: Question 8's focus on memory difficulties is particularly relevant in psychiatric populations where cognitive impairments may impact adherence, enhancing the scale's utility in such settings.

In conclusion, question 8 with its Likert scale plays a valuable role in the MMAS-8, enhancing its ability to measure medication adherence by contributing to its validity, reliability, and sensitivity to nuanced adherence challenges, particularly those related to memory.

​https://pmc.ncbi.nlm.nih.gov/articles/PMC6224788/
​https://www.sciencedirect.com/science/article/pii/S1697260014000623#:~:text=The%20eight%2Ditem%20Morisky%20Medication%20Adherence%20Scale%20(MMAS%2D8),has%20been%20widely%20used%20in%20various%20cultures.&text=The%20findings%20of%20this%20study%20suggest%20that,be%20used%20in%20a%20psychiatric%20outpatient%20setting.