A Hierarchical Linear Modeling (HLM) developer designs and implements statistical models that analyze data structures at multiple levels of hierarchy. Their work involves handling nested data, such as students within schools or employees within companies. They use HLM to understand the influence of different levels on the outcome variable, adjusting for individual and group-level variables. They also test hypotheses about cross-level interactions. Their responsibilities include data cleaning, coding, and creating algorithms in statistical software like R or SPSS. They interpret results and communicate findings to non-technical audiences, aiding in decision-making processes.