Final answer:
To analyze the relationship between TT4 and FTI levels in patients with thyroid disease, draw a scatter plot with TT4 as the independent variable and FTI as the dependent variable, calculate the least-squares line, assess the line's fit, and compute the correlation coefficient to determine the strength and direction of the relationship.
Step-by-step explanation:
To analyze the relationship between two variables, you first need to determine which variable should be the independent variable and which should be the dependent variable. For hormone levels and patients with thyroid disease, TT4 levels can be considered independent, and FTI levels the dependent variable.
To visualize the relationship, you draw a scatter plot of the data. Inspection of the scatter plot can indicate whether there is a relationship—points that cluster in a discernable pattern suggest a correlation.
The least-squares line can be calculated from the data points, providing an equation in the form ý = a + bx. Plotting this line on the scatter plot helps assess if a linear model fits the data well.
The correlation coefficient quantifies the strength and direction of the relationship between the variables. A significant coefficient implies a reliable relationship that is not due to random chance. The scatter plot provides additional context, such as the presence of outliers or if a non-linear model, like a curve, might be more appropriate.