KEY FEATURES: Introduces students to developing research questions and shows their importance in driving research design. Rarely taught topics, such as how to enter and clean data, offer students information missed in both research methods and statistics courses. Shows how to write up survey results for academic, business and nonprofit reports to alleviate the confusion students feel about how to write up findings. Rigorous treatment of sampling focuses on many sampling issues from probability theory to weighting. Offers the process of actually conducting a survey with advice on administering surveys, incentives, and improving response rates.

# How Do We Assess an Association Between Two Continuous Variables?

### How Do We Assess an Association Between Two Continuous Variables?

If both variables are continuous, we can graphically display the association using a scatter plot. From the scatter plot we can tell the direction of the association, the size of association from the slope, and whether or not the relationship is linear. We can measure size, direction, and statistical significance of the association using Pearson’s correlation coefficient.

The correlation coefficient is a numerical index that ranges from −1 to +1. A correlation of 0 means no association. A correlation of −1 means a perfectly correlated inverse association. That is, as the independent variable increases by one unit the dependent variable decreases by one unit. Lastly a correlation of +1 means a perfect positive association. ...