Growth Rates

Growth Rate

The growth rate gt of a variable X at time t is given by,

gt=XtXt1Xt1

This means the ratio of consecutive terms is given by,

1+gt=XtXt1

Growth Rate of Product

The growth rate gt of the product of variables X and Y at time t is given by,

gt=XtYtXt1Yt1Xt1Yt1=(1+gx)(1+gy)1gx+gy

Annualized Growth Rate

The annualized growth rate gt of a variable X at time t is given by,

gt=(1+XtXt1Xt1)n1n(1+XtXt1Xt1)

where n is the number of samples per year.

For monthly data, n=12.

For quarterly data, n=4.

Logarithm & Growth Rate

The growth rate gt of a variable X at time t is related to the natural logarithm of the variable:

log(Xt)log(Xt1)=log(1+gt)gt

The growth rate gt of the product of variables X and Y at time t is related to the natural logarithm of the variable:

log(XtYt)log(Xt1Yt1)=log(1+gx)+log(1+gy)gx+gy