[R] Heteroscedastic data due to responses at one factor level being too low to measure and assumed to be 0?

[Dr. Leigh S. Sutherland]

Hello all,

I have a 3-factor experimental design.
The response is the load to break an adhesive joint.

I have a question about Heteroscedastic data ('non-uniform variability',
Google told me that's what it's called - I'm not a statistician, just an
engineer)

*In essence:*

   - At one level of a factor the response values are so low to make them
   un-testable and they have to be assumed to be 0


   - However this gives no variability at that level since all responses
   are 0, (although in reality they may well have similar variability as at
   other levels).


   - This gives heteroscedastic data across the levels of the factor


   - What implications does this have for stats tests that are sensitive to
   Heteroscedastic data?


   - If I need to do anything, what can I do? can I 'superimpose' the same
   variability on level 1 results to give artificial variable values 'around'
   0kg? (this would not at all invalidate the data's validity)

Thanks,
Leigh

-- 
Leigh Sutherland

Centre for Marine Technology and Ocean Engineering (CENTEC)
Instituto Superior Técnico
Av. Rovisco Pais
1049-001 LISBOA
PORTUGAL

Tel: +351 218 417 947

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