The occurrence rate of hot Jupiters from the Kepler transit survey is roughly half that of radial velocity surveys targeting solar neighborhood stars .
One hypothesis to explain this difference is that the two surveys target stars with different stellar metallicity distributions .
To test this hypothesis , we measure the metallicity distribution of the Kepler targets using the Hectochelle multi-fiber , high-resolution spectrograph .
Limiting our spectroscopic analysis to 610 dwarf stars in our sample with \log { g } > 3.5 , we measure a metallicity distribution characterized by a mean of [ M/H ] _ { mean } = -0.045 \pm 0.009 , in agreement with previous studies of the Kepler field target stars .
In comparison , the metallicity distribution of the California Planet Search radial velocity sample has a mean of [ M/H ] _ { CPS,mean } = -0.005 \pm 0.006 , and the samples come from different parent populations according to a Kolmogorov-Smirnov test .
We refit the exponential relation between the fraction of stars hosting a close-in giant planet and the host star metallicity using a sample of dwarf stars from the California Planet Search with updated metallicities .
The best-fit relation tells us that the difference in metallicity between the two samples is insufficient to explain the discrepant Hot Jupiter occurrence rates ; the metallicity difference would need to be \simeq 0.2-0.3 dex for perfect agreement .
We also show that ( sub ) giant contamination in the Kepler sample can not reconcile the two occurrence calculations .
We conclude that other factors , such as binary contamination and imperfect stellar properties , must also be at play .