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Hazard Rate Function?

I am trying to do the following question:

The lifetime X (in years) of an item has a rate function λX(t)=t2+t4fort>0λX(t) = t^2 + t^4 \,for\, t > 0. What is the probability that
a) an item survives to age 1?
b) an item’s lifetime is between .5 and 1.5?
c) a 1/2 year old item will survive to age 1?
d) Now suppose the rate has doubled and let Y be the new lifetime with respect to the rate function 2λX(t)2\lambda_{X}(t).
What is P(Y>1Y>.5)P(Y > 1|Y > .5)?

I'm not sure how to tackle this question. In my book it says that the hazard rate function is defined by λ(t)=f(t)Fˉ(t)whereFˉ=1F\lambda(t)=\frac{f(t)}{\bar F(t)} \, where \bar F = 1 - F but the rate function we are given isn't similar to this form? I suppose I'm suppose to use the rate function in the exponential distribution. The book gives a very small explanation about hazard rate functions, and only one example so I'm having a hard time understand it. Please help!
(edited 8 years ago)
Original post by aspiring_doge
I am trying to do the following question:

The lifetime X (in years) of an item has a rate function λX(t)=t2+t4fort>0λX(t) = t^2 + t^4 \,for\, t > 0. What is the probability that
a) an item survives to age 1?
b) an item’s lifetime is between .5 and 1.5?
c) a 1/2 year old item will survive to age 1?
d) Now suppose the rate has doubled and let Y be the new lifetime with respect to the rate function 2λX(t)2\lambda_{X}(t).
What is P(Y>1Y>.5)P(Y > 1|Y > .5)?

I'm not sure how to tackle this question. In my book it says that the hazard rate function is defined by λ(t)=f(t)Fˉ(t)whereFˉ=1F\lambda(t)=\frac{f(t)}{\bar F(t)} \, where \bar F = 1 - F but the rate function we are given isn't similar to this form? I suppose I'm suppose to use the rate function in the exponential distribution. The book gives a very small explanation about hazard rate functions, and only one example so I'm having a hard time understand it. Please help!


You might like to look at the Wikipedia article on Survival Analysis, as it has all the formulae laid out there. But for the mean time, if the instantaneous hazard function is λ(t) \lambda(t) the first thing you need to calculate is the cumulative hazard function given by

Λ(t)=0tλ(u)du \displaystyle \Lambda(t) = \int_{0}^{t} \lambda(u) \mathrm{d} u

as the survival function (the probability that something survives for t or longer) is given by:

S(t)=exp(Λ(t)) \displaystyle S(t) = \exp \left( - \Lambda(t) \right)

Everything else in the question should be a routine use of this function.

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