There are two types of ERROR that we will dealing during conducting hypothesis testing; TYPE I ERROR: The probability of rejecting the Ho when Ho is TRUE. TYPE II ERROR: The probability of accepting the Ho when Ha is TRUE. TYPE I ERROR is serious form of error thus, it is denoted by alpha and is commonly referred as the SIGNIFICANCE LEVEL. TYPE II ERROR is usually denoted by beta where 1-beta is the POWER OF THE TEST. POWER OF THE TEST is the probability of rightly rejecting Ho when it is FALSE. In order words, we are RIGHT on deciding to accept Ha as our decision. There are some factors need to be considered when looking into the power of the test; When the significance level or a is made smaller, then the power will be decreases. In condition where the standard deviation of individual observation increases, the power will be decreases. By increasing sample size, then the power will be increasing too. The power of the test will be increases if the alternative me