Since the probit function
is non-linear, the effect of a unit increase on the probability will vary depending on the point on the distribution.
Table 6 Results for Probit Function
Variables Model l Model 2 Model 3 Constant 32.
Due to the sigmoidal shape of the probit function
, it should be noted that the calculated marginal effects at the means are likely to become smaller with successive incremental increases in government benefit income (Aldrich and Nelson, 1984).
Although it is unknown a priori which people will eventually make the transition, a probit function can be estimated to describe the probability that any individual will do so.
The probit function is static by design, because it seeks to measure the unchanging portion of addictive propensity, so it can not follow changing cigarette prices.
To correct this, we first estimate a probit function
to predict the probability that an individual is in the wage sector.
In this process they also estimate probit functions
, which attempt to explain factors determining probability of starting school.