#### Answer

1. Effect size
2. Sample size
3. Sample variability
4. The significance level a.

#### Work Step by Step

1. The larger the difference in the 2 means, the more likely that you will be able to reject the null hypothesis.
2. The lager the sample size, the smaller the standard error.
3. The smaller the variability, the better. The only way to minimize the variability is to reduce the random error caused by sloppy data collection.
4. The longer the value of a, the more likely you are to reject the null hypothesis (whether it is true or false).