# How to decompose a distribution with two peaks?

I'm modeling saving account's amount, whose change looks like a log-normal distribution. It means suppose $y$ is total saving account's amount; $x = \ln(y)$ is the natural log; $dx$, the daily change, seems follows normal distribution.

However, $dx$ seems has 2 peaks, one is high and a bit less than 0, one is lower and bigger than 0.

The reason could be that people are likely to frequently withdraw little amount of money, e.g. weekly withdraw 200 bucks for everyday expense, and deposit more money less frequently, e.g. monthly deposit the paycheck.

Now the question is, how could this distribution be decomposed?

Seems I can't decompose it to two normal distribution, as two independent normal distribution's sum is still a normal distribution.

Any suggestion?

• "seems i can't decomposite it to 2 normal distribution, as 2 independent normal distribution's sum is still a normal distribution" -- you're looking at something more like a mixture, not a convolution. Each change is not a sum of a deposit and a withdrawal, it's either one or the other. – Glen_b Jul 25 '13 at 6:04