tokens: have a constant absolute magnitude of −7 mag. The investigation on decline times for all novae in the catalogue indicates that the novae with D- and J- type light-curve shapes may not have linear decline. If so, only considering the decline times ( t 2 or t 3 ) may not characterize the absolute magnitude at outburst maximum and the decline well. All of these arise uncertainties when using of MMRD relation if the type of nova is not clarified. Furthermore, the luminosities of novae may differ depending on their stellar populations or their evolutionary states, i.e. on the stellar age and metallicity. For the scatters found in other distance indicators, e.g. Cepheids, it has been suggested that a different metallicity of the host galaxy may significantly affect the zero-point of the relation (Freedman et al. 2001 ). In this case, there is a possibility on any environmental dependence on MMRD relations as well. Since our and the other studies in literature depend on disc novae in the Galaxy, the contribution of other populations (bulge, halo, even thick disc) is not well known. Our study does not dispel the concerns regarding the validity the MMRD relation, but has raised open questions. To understand the MMRD relation better, the novae in galaxies, which have reliable distances (and extinctions), should be studied with high quality photometric and spectroscopic data. A larger sample of them would also be very welcome as well as corresponding parameters and well-determined light curves that allow us to classify their light-curve shapes. Our catalogue may also help to investigate the nature of MMRD diagrams in the long-term. Studying the MMRD relation is important to understand the origin of the nova eruption itself, besides using it as a tool to estimate absolute magnitudes. In this study, we did not find any signs that the spectral classification represents the stellar population of the Galactic novae, as suggested by Della Valle Livio ( 1998 ). However, our decline time histogram implies that the He/N+Hybrid novae are fast systems with a peak time at t 3 = 13 d, while the slow Fe ii novae have a peak decline time at t 3 = 42 d. In contrast to the suggestion of Della Valle Livio ( 1998 ), we found that both Fe ii and He/N novae or fast and slow novae are located in the whole range of vertical distances, but mainly concentrated throughout the Galactic disc. The differences between the results in these two studies may arise from the samples used in the analyses. The sample in Della Valle Livio ( 1998 ) contains a smaller number of novae with spectral classification, which reach only to a vertical distance of ∼2 kpc, whereas our sample have much more systems reaching up to two times farther in vertical direction from the Galactic plane. A relatively large number of slow novae located close to the Galactic plane and fast novae farther from Galactic plane must have been undetected in their analyses. The approach proposed by Della Valle Livio ( 1998
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