Why was the declaration of independence to be read aloud throughout the colonies?

Because it was an important part of the colonies' identity.

Also, not all the colonists had access to copies or could even read

this null effect is caused by a weak manipulation and ineffective internal validity. in a scientific study, as the one dr. morimoto is trying to perfom, internal validity refers to the confidence placed in the cause-effect relationship and to how well an experiment is done and able to eliminate confounding variables.