Elution Rate - Alkanes VS Alkenes in Gas Chromatography

Some references say that alkanes elute faster than alkenes, whereas in my textbook the higher volatility of alkenes means they elute faster than alkanes. This is for gas chromatography.

Alkenes are more polar than alkanes due to more electron-withdrawing $\text{sp}^2$-hybrid orbitals (more s-character draws electrons closer to nucleus).

Can someone please clarify - bit confused.

Ladislav Sojak published a freely available 35-page review Separation and identification of isomeric hydrocarbons by capillary gas chromatography and hyphenated spectrometric techniques in Petroleum & Coal, 2004, 4(3), 1-35 (PDF). You might want to have a look at this article on the effect of having non-terminal $\ce{C=C}$ double bonds and cis-trans isomers of longer alkenes, which therefore have significantly different shapes.