The observational properties (fractionary mass of gas, metallicity and colours) of a sample of dwarf irregular and magellanic type galaxies are discussed in the light of the stochastic self propagating star formation model of Gerola et al. (1980). To this aim, one-zone model galaxies are presented which take into account both the bursting mode of star formation and infall of unenriched gas. The comparison with the observational data shows that the high dispersion in the properties of these galaxies cannot be explained by the stochastic mechanism alone. Three possible ways out are indicated, namely variations in the metal yield, variations in the ratio of the star formation to mass accretion rates, and finally variations in the ratio of star formation to galactic wind rates.