Understanding how individuals perceive and use ideological scales is crucial for estimating voter and party positions in latent political space across political research disciplines. Existing research shows that individuals differ in the way they use ideological scales, and suggests ways to correct for such DIF or bias. However, we know little about systematic patterns of variation in scale usage across time. While most research assumes that cross-temporal changes in perceptions reflect changes in actual positions, we lack conceptual and methodological clarity about how to differentiate changes in actual positions from changes in the scales that individuals use to perceive and report positions.

The paper examines temporal and contextual variations in scale usage by analysing two German panel datasets in a novel way. To identify contextual changes in ideological scale usage, we apply a scaling model based on left-right self- and party-placements, and provide causal evidence through temporal variation (unexpected events design) and contextual stimuli (divergences in individual party placements based on different experimental scenarios).

The results show that ideological scales are not static benchmarks, but are subject to considerable fluctuation, with significant variations across temporal and contextual factors. Estimates of ideological scales based on perceptions will be biased if they do not take into account temporal changes in scale perceptions, for example caused by the entry of new parties. Perceived shifts to the left or right often reflect changes in scale perceptions and political system characteristics rather than actual positional shifts, with implications for both political research and public discourse.