Sea star wasting disease kills sea stars (i.e., starfish) and has no known cause. It is currently a major problem on the West Coast and many sea stars are infected and dying. Consider a study in which a researcher is interested in whether susceptibility varies between the species. He travels to a site known to show wasting and counts the numbers of healthy and wasting individuals from three different species. His data is shown in the histogram below.

-To determine whether there appears to be a statistically significant relationship between species and prevalence of wasting disease he would conduct a χ² analysis. When performing this analysis, which of the values below is closest to the number of degrees of freedom he would use?

Question

Sea star wasting disease kills sea stars (i.e., starfish) and has no known cause. It is currently a major problem on the West Coast and many sea stars are infected and dying. Consider a study in which a researcher is interested in whether susceptibility varies between the species. He travels to a site known to show wasting and counts the numbers of healthy and wasting individuals from three different species. His data is shown in the histogram below.

-To determine whether there appears to be a statistically significant relationship between species and prevalence of wasting disease he would conduct a χ² analysis. When performing this analysis, which of the values below is closest to the number of degrees of freedom he would use?

Quizplus · Accepted Answer

A chi-square test of independence has (r-1) * (c-1) degrees of freedom, where r is the number of rows and c is the number of columns in the contingency table. In this case, the contingency table has 2 rows (species) and 2 columns (prevalence of wasting disease), so the degrees of freedom are (2-1) * (2-1) = 1.

Sea Star Wasting Disease Kills Sea Stars (I