The official population of some states increased, while the populations of others decreased. As a result, the number of U.S. representatives allocated to these states changed.

What type of interaction does the underlined phrase show?

The underlined phrase shows a cause and effect interaction. The change in population led to a change in the number of U.S. representatives allocated to the states.

The underlined phrase "the number of U.S. representatives allocated to these states changed" shows a cause and effect interaction.