This question is related to How to analyze curvilinear seasonal data

I have data like following:

subjectID, month, vnum1, age, gender
1          1       5    10      1 
2          1       6    15      2
3          2       6    18      2
...

I have one continuous variable (called vnum1) which is showing a curvilinear relation with month of the year (lower in summer months). However, I have 2 other variables also- age and gender. I have to determine if the curvilinear relation of vnum1 with month is independent of age and gender. How can I test this. Thanks for your help.

This question is related to How to analyze curvilinear seasonal data

I have data like following:

subjectID, month, vnum1, age, gender
1          1       5    10      1 
2          1       6    15      2
3          2       6    18      2
...

I have one continuous variable (called vnum1) which is showing a curvilinear relation with month of the year (lower in summer months). However, I have 2 other variables also- age and gender. I have to determine if the curvilinear relation of vnum1 with month is independent of age and gender. How can I test this. Thanks for your help.