Verify regression model with control variable Z

## Arguments

- n_obs
number of observations

- sdx
standard deviation of X

- sdy
standard deviation of Y

- sdz
standard deviation of Z

- sdcv
sd between C and V

- rxy
correlation coefficient between X and Y

- rxz
correlation coefficient between X and Z

- rzy
correlation coefficient between Z and Y

- rcvy
correlation coefficient between V and Y

- rcvx
correlation coefficient between V and X

- rcvz
correlation coefficient between V and Z