One major difference between the Assembly and the Council of 500?

The assembly was attended by all male citizens of Athens, Councils of 500 was only attended by the Citizen's Representatives.

Explanation:

In the past, Athens held the Assembly around 40 times a year. All male citizens were expected to gathered in one place to discuss various issues such as, taxation, war/security, religion and treaties/alliance with other nations.

Councils of 500 on the other hand, was a attended by representatives that were elected from the pool of citizens. They chose these representatives using a lottery system. (It's based on luck rather than through voting)

The third-variable rule

Explanation:

We will have a better understanding of the third-varibale rule or problem, when we understand correlation.

We can definition correlation as being always low on internal validity.

It is the possibility that some extraneous variable is responsible for the correlation that was found between the two variables of interest this is because it caused both of them.

It can take its extreme form.

Here, the third variable can be said to be the entire cause of the correlation between the two variables of interest and there's no causal relationship between them at all. This would make the correlation between the two variables of interest spurious.