If everything else stays the same, the margin of error can be reduced by (select all that are true) :

a. increasing confidence level

b. decreasing sample size

c. increasing sample size

d. decreasing confidence level

c. increasing sample size

d. decreasing confidence level

Step-by-step explanation:

Formula for margin of error :

, = Population standard deviation.

, s= sample standard deviation.

, p= sample proportion.

Here z and t are critical values.

n= sample size.

Margin of error has critical t-value of z-value in the numerator .

⇒ Margin of error is proportional to the critical value.

⇒ Margin of error is proportional to the confidence level.

(The critical t-value of z-value is proportional the confidence level increases.)

So , Margin of error can be reduced by decreasing confidence level.

Also , Margin of error has square root of the sample size in the denominator.

⇒ Margin of error is inversely proportional to the sample size.

So , Margin of error can be reduced by increasing sample size.

Hence, the correct options area :

c. increasing sample size

d. decreasing confidence level