  Laboratory courses represent a unique and potentially important component of
the undergraduate physics curriculum, which can be designed to allow students
to authentically engage with the process of experimental physics. Among other
possible benefits, participation in these courses throughout the undergraduate
physics curriculum presents an opportunity to develop students' understanding
of the nature and importance of experimental physics within the discipline as a
whole. Here, we present and compare both a longitudinal and pseudo-longitudinal
analysis of students' responses to a research-based assessment targeting
students' views about experimental physics -- the Colorado Learning Attitudes
about Science Survey for Experimental Physics (E-CLASS) -- across multiple,
required lab courses at a single institution. We find that, while
pseudo-longitudinal averages showed increases in students' E-CLASS scores in
each consecutive course, analysis of longitudinal data indicates that this
increase was not driven by a cumulative impact of laboratory instruction.
Rather, the increase was driven by a selection effect in which students who
persisted into higher-level lab courses already had more expert-like beliefs,
attitudes, and expectations than their peers when they started the lower-level
courses.
