90The information that you'd need in determining sample size when the standard deviation is unknown is:
z-value for the given level of confidence ⇒ The level of confidence is 90% and the z-value by convention is 1.645
The margin error (E) = 4%
The proportion of the population that you'd expect to vote for Yi. If this information isn't provided, use 50%. We call this value, p, the probability of success.
The probability of not success is q = 1 - 0.5 = 0.5
STEP 1:
Half the margin error = 0.04 ÷ 2 = 0.02
STEP 2:
Multiply the probability of success by the probability of fail = 0.5 × 0.5 = 0.25
STEP 3:
Divide z-score by half of E = 1.645 ÷ 0.02 = 82.25
Then square the answer = 82.25² = 6765 rounded to the nearest integer)
STEP 4:
Multiply the answer from STEP 2 by the answer from STEP 4
0.25 × 6765 = 1691 (rounded to the nearest integer)
Answer: Minimum Sample Size is 1691
