The aim of the study is to assess whether attending to nursery is associated with high frequency of respiratory infections.
It is useful to compare proportions of infection by category of assistance to the nursery, we do this by comparing percentages of rows and calculating the Chi square test for association between these two variables.
In this example, the variable result is respiratory infection (dependent variable) and assistance to the nursery as the exposure variable (independent variable), which explains the frequency of infection.
To measure the association between exposure and outcome in a 2 x 2 table we can calculate the risk ratio (RR) or odds ratios (OR).