I have some evidence showing that likelihood of breakdown is influenced by the following variables:

sex (of owner)

age (of owner)

age (of vehicle)

amongst others.

Regression can be used to estimate the probability of breakdown at a given time based on the some known assumptions about the vehicle owner.

I have hit a stumbling block in the following situation:

when a previous owner (say a 53yo male) gives the vehicle to a new owner (say a 20yo female).

Intuitively I feel that the usage of the previous owner will affect the state of the vehicle and hence the probability of the new owner breaking down will be altered but I am unsure how to describe this mathematically.

I had considered averaging:

i.e. if male is represented '1' and female '0' then in this situation VAR is '0.5'

but this is just guesswork.

Any help would be appreciated.