A reasonable summary of the data might be provided by relating the score S_i given by S_i = 1 if never, S_i = 2 if irregular, S_i = 3 if fall and winter, and S_i = 4 if whole year. What method can be used to relate mean BMD to this score variable? Perform a test of significance using this method?

Assess whether the mean BMD varies significantly among the four groups at the 5% level.