What are the preconditions of ANOVA hypothesis? What is the main effect? What is the interactive effect?

Dependent variables obey normal distribution at different levels of independent variables.

Under different levels of independent variables, the variance of dependent variables is homogeneous.

Main effect and interaction effect: the main effect is the independent variable of a single factor, and the interaction effect is the interaction of two independent variables.

For example, weather and swimming skills will affect whether a person will drown, so the formula of the main influence of drowning is:

Drowning probability = whether the weather is hot or not+strong swimming ability+combination of weather and swimming ability+other factors.

The first two are main effects, the third is interaction, and the last is random factors.

May think that interaction is not the result of the combination of the previous main effects? Not necessarily. For example, the probability of drowning in cold weather will be low (only there are many people swimming in summer), and the probability of drowning will be low if the swimming skill is strong; It is possible that people with strong swimming ability are more likely to drown when it is cold (people who eat vegetables don't swim, people with strong swimming cramps in winter, etc.)