Chi-square for trend tests for the presence of a trend in studies where a series of increasing or decreasing exposures is being examined.Sample Size and Power calculations include Population Survey, Cohort or Cross-Sectional, and Unmatched Case-Control.05, this means there is no interaction effect between sunlight and water.Six types of calculations are available in StatCalc: The p-value for the interaction between sunlight and water is. 05, this means watering frequency also has a statistically significant effect on plant growth. 05, this means sunlight exposure has a statistically significant effect on plant growth. The p-value associated with sunlight is.Here’s how to interpret the output of the ANOVA: However, we can also perform a two-way ANOVA to formally test whether or not the independent variables have a statistically significant relationship with the dependent variable.įor example, the following code shows how to perform a two-way ANOVA for our hypothetical plant scenario in R: #make this example reproducible Plotting the means is a visualize way to inspect the effects that the independent variables have on the dependent variable. Rather, there is an interaction effect between the two independent variables. In other words, sunlight and watering frequency do not affect plant growth independently. The two lines are not parallel at all (in fact, they cross!), which indicates that there is likely an interaction effect between them.įor example, this means the effect that sunlight has on plant growth depends on the watering frequency. In the previous plot, the two lines were roughly parallel so there is likely no interaction effect between watering frequency and sunlight exposure. If the two lines in the plot are not parallel, there is an interaction effect.If the two lines in the plot are parallel, there is no interaction effect.To determine if there is an interaction effect between the two independent variables, we simply need to inspect whether or not the lines are parallel: The mean growth for plants that received low sunlight and weekly watering was about 5.8 inches.The mean growth for plants that received low sunlight and daily watering was about 5.3 inches.The mean growth for plants that received high sunlight and weekly watering was about 9.6 inches.The mean growth for plants that received high sunlight and daily watering was about 8.2 inches.Here’s how to interpret the values in the plot: When we use a 2×2 factorial design, we often graph the means to gain a better understanding of the effects that the independent variables have on the dependent variable.įor example, consider the following plot: Visualizing Main Effects & Interaction Effects Does the effect of watering frequency on plant growth depend on the amount of sunlight?.Does the effect of sunlight on plant growth depend on watering frequency?.Interaction Effects: These occur when the effect that one independent variable has on the dependent variable depends on the level of the other independent variable.įor example, in our previous scenario we could analyze the following interaction effects: We can find the mean plant growth of all plants that were watered weekly.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |