Which type of study involves comparisons between groups without formal manipulation and random assignment?

The chosen answer identifies a type of study that focuses on understanding relationships or differences among groups without the direct intervention or manipulation of variables, which is characteristic of nonexperimental research. In this context, explanatory nonexperimental studies aim to describe or explain phenomena based on observational data rather than altering conditions or assigning participants to different groups at random.

In this type of study, researchers might collect data from different groups that naturally differ on certain characteristics or experiences. By comparing these groups, the researchers can gain insights into potential correlations or trends, although they cannot infer causation due to the lack of controlled manipulation or randomization.

In contrast, an experimental study relies on the deliberate manipulation of variables and typically involves random assignment to ensure that any observed effects can be attributed to the intervention, rather than pre-existing differences between groups. Longitudinal studies focus on data collected over a period to observe changes over time, while cross-sectional studies provide a snapshot of data at a single point in time. Both the longitudinal and cross-sectional designs, like experimental research, do not fit the criteria of comparing groups without manipulation or random assignment, making explanatory nonexperimental the best fit for the description provided.