Final answer:
The idea that others' opinions about us in an online context are more believable relates to Charles Cooley's looking-glass self theory, which is not directly listed in the provided options but relates closely to symbolic interactionism in sociology.
Step-by-step explanation:
The sentiment that what others say about you online is more believable than what you say about yourself aligns with Charles Cooley's theory of the looking-glass self. This concept suggests that our self-image is shaped by how we believe others perceive us. When people respond positively to our actions, we are likely to continue behaving in that manner, reinforcing the idea that external perceptions play a significant role in shaping our self-concept.
In an online context, the looking-glass self is particularly potent as feedback is often immediate and widespread. It is not precisely captured by the options provided in the initial question (Social Comparison Theory, Self-Perception Theory, Elaboration Likelihood Model, or Attribution Theory), but if we had to choose the closest among these, Social Comparison Theory seems somewhat related as it's about comparing oneself to others. However, the question as posed does not exactly fit these theories. Instead, one could consider this question within the scope of symbolic interactionist perspectives in sociology, which focus on the meanings individuals impose upon themselves and others within social interactions.