These study tips are designed to clarify key points and help you to avoid errors that students commonly make. Review the Tips for Success as you study each chapter and review them again after you have studied each chapter.

1. Before beginning Chapter 2, you should be sure you are comfortable with the key terms of variable, score, and value that we considered in Chapter 1.
2. Think of each formula as a statistical recipe. The ingredients of each formula are written using statistical symbols. Before you use each formula, be sure you know what statistical term each symbol stands for. (For example, as you learn shortly, the symbol “N” means “number of scores”.) Then, step by step, carefully follow the formula to come up with the end result. As with any recipe, it may take a couple of attempts to master; but after that, you should get perfect results every time. Also, don’t forget to focus on understanding the logic behind each formula.
3. When an answer is not a whole number, we suggest that you use two more decimal places in the answer than for the original numbers. In the example on page 41, the original numbers did not use decimals, so we rounded the answer to two decimal places.
4. The sum of the squared deviations is an important part of many of the procedures you learn in later chapters, so be sure you fully understand it, as well as how it is figured.
5. Always check that your answers make intuitive sense. For example, when looking at the scores in the dreams example on page 52, a standard deviation – which, roughly speaking, represents the average amount the scores vary from the mean – of 2.57 makes sense. If your answer had been 21.23, however, it would mean that, on average, the number of dreams varied by more than 20 from the mean of 6. Looking at that group of scores, that just couldn’t be true.
6. Notice in Table 2-2 that the deviation scores (shown in the third column) add up to 0. The sum of the deviation scores is always 0 (or very close to 0, allowing for rounding error). So, to check your figuring, always sum the deviation scores. If they do not add up to 0, do your figuring again.
7. One of the most common errors statistics students make when figuring the median is to forget to first line the scores up from lowest to highest