Friday, March 8, 2013

linear probability model

Definition:

Linear probability model is one of the econometric model where the dependent variables having the probability between 0 and 1. There are two things related to Linear probability model

I) Logit

II) Probit

Logit is one of the important part in linear probability model. The Logit function is nothing but the inverse function of logistic which is used in mathematics.
Probit model is a popular method in linear probability model. This model is established using standard maximum likelihood procedure.

Explanation for Linear probability model:


The declining model places no limitation on the values that the independent variables take on. They may be continuous, period level, they may be only positive or zero or they may be dichotomous variable (1=male, 0= female)

The dependent variable is implicit to be continuous. There is no constraint on the IVs; the DVs must be free to range in value from negative infinity to positive infinity

We put into practice, only a small variety of Y values will be observed. Because it is also the case that only a small range of X values will be observed. The best guess on continuous interval measurement is frequently not problematic, That is, even though degeneration assumes that Y can range from negative infinity to positive infinity. It regularly won’t be too much of a disaster if. It really only ranges from 1 to 17

Y can only take two values if Y can equal to 0 or 1 then

E (Yi)= 1 x P (Yi = 1) + 0 x P (Yi = 0) =P (Yi = 1)

Final equation is: E (Yi) = P (Yi) = α + Σ β k X k


Examples for linear probability model:


The yield of apple in an acre of apple plantation depends on various types of agriculture practice (treatments). An experiment may be planned where various ploys are subjected to one  out of two possible treatment over a period of time .The yield of tea before the  application of treatment is also recorded .A  Model for post treatment yield(y) is

y = `beta` 0+ `beta`1 x 1+ `beta` 2 x 2 + `in`

Where the binary variables x1 represent the treatment type and the real valued variable x2 is the pre treatment yield. The error term mainly consists of unaccounted factors such as soil type or the inherent differences in apple bushes

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