It is very difficult to establish a causal connection between two ...

[rayancarla1]

It is very difficult to establish a causal connection between two variables without the use of anything except a __________.
 Fill in the blank(s) with correct word

Question 2

The __________ the number of confounding factors that can be ruled out, the __________ convincing the evidence for a causal connection.
 Fill in the blank(s) with correct word

[qytan]

Answer to Question 1

RANDOMIZED EXPERIMENT

Answer to Question 2

GREATER AND MORE; OR FEWER AND LESS.