Explanation

On the run/off the run is NOT typically considered an illiquidity factor for equity returns because:

• On the run/off the run primarily applies to government bonds, where newly issued bonds (on-the-run) trade more actively than older issues (off-the-run)
• This distinction is specific to fixed income markets, not equity markets

The other options ARE valid illiquidity factors for equities:

• Trading Frequency: How often a stock trades affects liquidity
• Bid-ask spread: Wider spreads indicate lower liquidity
• Quote size: The size of orders that can be executed without moving prices

Equity illiquidity factors typically include measures like trading volume, bid-ask spreads, price impact, and market depth, but not the on/off-the-run distinction which is bond-specific.