# Do I use the bid or ask time series to build a model to predict forex and for a backtester

In my tick feed I get real-time bid and ask prices like below from oanda.

My question is this. Lets assume I build a time series model to buy eur/usd in the Oanda UI manually. If I were to build that time series model do I use bids or asks? If I were to build a backtester do I evaluate on bid or ask? If I sell then do I use the ask series to build a model?

So I posit this assuming I make a 5-minute forecast with a 1-minute rolling window:

• build a time series model from bids data
• given the current minute forecast 5 minutes ahead
• if my models predict to buy because I forecast a 10 pip increase I set e.g. a take profit and a stop loss
• look at the max high over the future 5 minutes and test if my take profit or stop loss was triggered using the high and low in the OHLC data.

In sum so I build and evaluate models based on bid, ask or test both? Really interested only in what the consensus is for using bid or ask data. Or there some smoothing that's take some weights avg of the two?

Thanks

{
"type": "PRICE",
"time": "2020-03-09T16:00:00.865263948Z",
"bids": [{
"price": "1.14197",
"liquidity": 10000000
}],
"price": "1.14210",
"liquidity": 10000000
}],
"closeoutBid": "1.14197",