Standard Error for sample mean estimation of the population

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					Standard Error for sample mean estimation of the population mean:


         
                  S
                       
                               (x       i    x ) 2 /(n  1)
S    x
                  n                             n
Standard Error for sample proportion estimation of the population proportion:

                      p(1  p)
Sp                         n

Standard Error for sample slope estimation of population slope coefficients:
(For k=2 independent variables)
                                                                       A

                  
                                                    e      2
                                                            i
SE
                            (x
             ˆ
                                          x1 )2 (1  r12 ) n  2  1
             B1                                         2
                                    1i


                           B
                                                       C               D

How can we make our common-sized error smaller when estimating slopes?

A:


B:


C: r   12   is the correlation between our two independent variables




D: