Context :

Aims : We have performed a comprehensive multiwavelength analysis of a sample of 20 starburst galaxies that show a substantial population of very young massive stars , most of them classified as Wolf-Rayet ( WR ) galaxies .
In this paper , the forth of the series , we present the global analysis of the derived photometric and chemical properties .

Methods : We compare optical/ NIR colours and the physical properties ( reddening coefficient , equivalent widths of the emission and underlying absorption lines , ionization degree , electron density , and electron temperature ) and chemical properties ( oxygen abundances and N/O , S/O , Ne/O , Ar/O , and Fe/O ratios ) with previous observations and galaxy evolution models .
We compile 41 independent star-forming regions –with oxygen abundances between 12+log ( O/H ) = 7.58 and 8.75– , of which 31 have a direct estimate of the electron temperature of the ionized gas .

Results : According to their absolute B -magnitude , many of them are not dwarf galaxies , but they should be during their quiescent phase .
We found that both c ( H \beta ) and W _ { abs } increase with increasing metallicity .
The differences in the N/O ratio is explained assuming differences in the star formation histories .
We detected a high N/O ratio in objects showing strong WR features ( HCG 31 AC , UM 420 , IRAS 0828+2816 , III Zw 107 , ESO 566-8 and NGC 5253 ) .
The ejecta of the WR stars may be the origin of the N enrichment in these galaxies .
We compared the abundances provided by the direct method with those obtained through empirical calibrations , finding that ( i ) the Pilyugin method is the best suited empirical calibration for these star-forming galaxies , ( ii ) the relations provided by Pettini & Pagel ( 2004 ) give acceptable results for objects with 12+log ( O/H ) > 8.0 , and ( iii ) the results provided by empirical calibrations based on photoionization models are systematically 0.2 – 0.3 dex higher than the values derived from the direct method .
The O and N abundances and the N/O ratios are clearly related to the optical/ NIR luminosity ; the dispersion of the data is a consequence of the differences in the star-formation histories .
The L – Z relations tend to be tighter when using NIR luminosities , which facilitates distinguishing tidal dwarf galaxies candidates and pre-existing dwarf objects .
Galaxies with redder colours tend to have higher oxygen and nitrogen abundances .

Conclusions : Our detailed analysis is fundamental to understand the nature of galaxies that show strong starbursts , as well as to know their star formation history and the relationships with the environment .
This study is complementary –but usually more powerful– to the less detailed analysis of large galaxy samples that are very common nowadays .