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We present results of the analysis of 70 RR Lyrae stars located in the bar ofthe Large Magellanic Cloud (LMC). Combining spectroscopically determinedmetallicity of these stars from the literature with precise periods from theOGLE III catalogue and multi-epoch $K_{\rm s}$ photometry from the VISTA surveyof the Magellanic Clouds system (VMC), we derive a new near-infraredperiod-luminosity-metallicity (${\rm PL_{K_{\rm s}}Z}$) relation for RR Lyraevariables. In order to fit the relation we use a fitting method developedspecifically for this study. The zero-point of the relation is estimated in twodifferent ways: by assuming the value of the distance to the LMC and by usingHubble Space Telescope (HST) parallaxes of five RR Lyrae stars in the Milky Way(MW). The difference in distance moduli derived by applying these twoapproaches is $\sim0.2$ mag. To investigate this point further we derive the${\rm PL_{K_{\rm s}}Z}$ relation based on 23 MW RR Lyrae stars which had beenanalysed in Baade-Wesselink studies. We compared the derived ${\rm PL_{K_{\rms}}Z}$ relations for RR Lyrae stars in the MW and LMC. Slopes and zero-pointsare different, but still consistent within the errors. The shallow slope of themetallicity term is confirmed by both LMC and MW variables.  The astrometric space mission Gaia is expected to provide a huge contributionto the determination of the RR Lyrae ${\rm PL_{K_{\rm s}}Z}$ relation, however,calculating an absolute magnitude from the trigonometric parallax of each starand fitting a ${\rm PL_{K_{\rm s}}Z}$ relation directly to period and absolutemagnitude leads to biased results. We present a tool to achieve an unbiasedsolution by modelling the data and inferring the slope and zero-point of therelation via statistical methods.

New near-infrared period-luminosity-metallicity relations for RR Lyrae stars and the outlook for Gaia