bid & ask prices and technical indicators
If you are looking to go long (buy) you would use bid prices as this is what you will be matched against for your order to be executed and a trade to go through. If you are looking to go short (sell) you would use the ask prices as this is what you will be matched against for your order to be executed and a trade go through. In your analysis you could use either this convention or the midpoint of the two prices. As FX is very liquid the bid and ask prices would be quite close to each other, so the easiest way to do your analysis is to use the convention I listed above.
"Re: A trader when buying needs to buy at the ask price and when selling needs to sell   at the bid price. So how can a trade happen 'in between' the bid and ask? Saying the trade can happen ""in between"" the bid & ask is simplistic.  There is a time dimension to the market.  It's more accurate to say that an order can be placed ""in between"" the current best bid & ask (observed at time T=0), thus establishing a new level for one or the other of those quoted prices (observed at time T>0). If you enter a market order to buy (or sell), then yes, you'll generally be accepting the current best ask (or best bid) with your order, because that's what a market order says to do: Accept the current best market price being offered for your kind of transaction.  Of course, prices may move much faster than your observation of the price and the time it takes to process your order – you're far from being the only participant. Market orders aside, you are free to name your own price above or below the current best bid & ask, respectively. ... then one could say that you are placing an order ""in between"" the bid and ask at the time your order is placed.  However – and this is key – you are also moving one or the other of those quoted prices in the process of placing your above-bid buy order or your below-ask sell order. Then, only if somebody else in the market chooses to accept your new ask (or bid) does your intended transaction take place. And that transaction takes place at the new ask (or bid) price, not the old one that was current when you entered your order. Read more about bid & ask prices at this other question: (p.s. FWIW, I don't necessarily agree with the assertion from the article you quoted, i.e.: ""By looking for trades that take place in between the bid and ask, you can tell when a strong trend is about to come to an end.""  I would say: Maybe, perhaps, but maybe not.)" In the world of stock exchanges, the result depends on the market state of the traded stock. There are two possibilities, (a) a trade occurs or (b) no trade occurs. During the so-called auction phase, bid and ask prices may overlap, actually they usually do. During an open market, when bid and ask match, trades occur. I frequently do this on NADEX, selling out-of-the-money binary  calls. NADEX is highly illiquid, and the bid/ask is almost always from  the market maker. Out-of-the-money binary calls lose value quickly  (NADEX daily options exist for only ~21 hours). If I place an  above-ask order, it either gets filled quickly (within a few minutes)  due to a spike in the underlying, or not at all. I compensate by  changing my price hourly.  As Joe notes, one of Black-Scholes inputs is volatility, but price  determines (implied) volatility, so this is circular. In other words, you can  treat the bid/ask prices as bid/ask volatilities. This isn't as  far-fetched as it seems:  http://www.cmegroup.com/trading/fx/volatility-quoting-fx-options.html "According to Yahoo, AAPL was trading at $113.26 at 1:10 PM on 11/13/15, which is the approximate time of your option quote.  You provided a quote for AAPL at 4:15, and the stock happened to keep going down most of the that afternoon.  To make a sensible comparison, you need to take contemporary prices on both the stock and the option.  The quote on the option also shows the ""price"" being outside of the bid-ask range, which suggests that the option was trading thinly and that the last price occurred sometime earlier in the day.  If you use a price in the bid-ask range ($21.90-$22.30) and use the price of AAPL at the time of the put quote, you'll come up with a price that's much closer to your expectation." "First, I would like to use a better chart.  In my opinion, a close of day line chart obscures a lot of important information.  Here is a daily OHLC log chart:  The initial drop from the 1099.23 close on Oct 3 was to 839.8 intraday, to close at 899.22 on Oct 10.  After this the market was still very volatile and reached a low of 747.78 on Nov 20, closing only slightly higher than this.  It traded as high as 934.70 on Jan 6, 2009, but the whole period of Nov 24 - Feb 13 was somewhat of a trading range of roughly 800-900.  Despite this, the news reports of the time were frequently saying things like ""this isn't going to be a V shaped recovery, it is going to be U shaped.""  The roughly one week dip you see Feb 27 - Mar 9 taking it to an intraday low of 666.79 (only about 11% below the previous low) on first glance appears to be just a continuation of the previous trend.   However... The Mar 10 uptrend started with various news articles (such as this one) which I recall at the time suggested things like reinstating the parts of the Glass–Steagall Act of 1933 which had been repealed by the Gramm–Leach–Bliley Act.  Although these attempts appear to have been unsuccessful, the widespread telegraphing of such attempts in the media seemed to have reversed a common notion which I saw widespread on forums and other places that, ""we are going to be in this mess forever, the market has nowhere to go but down, and therefore shorting the market is a good idea now.""  I don't find the article itself, but one prominent theme was the ""up-tick"" rule on short selling: source From this viewpoint, then, that the last dip was driven not so much by a recognition that the economy was really in the toilet (as this really was discounted in the first drop and at least by late November had already been figured into the price).  Instead, it was sort of the opposite of a market top, where now you started seeing individual investors jump on the band-wagon and decide that now was the time for a foray into selling (short).  The fact that the up-tick rule was likely to be re-instated had a noticeable effect on halting the final slide." The Art of Short Selling by Kathryn Stanley providers for many case studies about what kind of opportunities to look for from a fundamental analysis perspective. Typically things you can look for are financing terms that are not very favorable (expensive interest payments) as well as other constrictions on cash flow, arbitrary decisions by management (poor management), and dilution that doesn't make sense (usually another product of poor management). From a quantitative analysis perspective, you can gain insight by looking at the credit default swap rate history, if the company is listed in that market. The things that affect a CDS spread are different than what immediately affects share prices. Some market participants trade DOOMs over Credit Default Swaps, when they are betting on a company's insolvency. But looking at large trades in the options market isn't indicative of anything on its own, but you can use that information to help confirm your opinion. You can certainly jump on a trend using bad headlines, but typically by the time it is headline news, the majority of the downward move in the share price has already happened, or the stock opened lower because the news came outside of market hours. You have to factor in the short interest of the company, if the short interest is high then it will be very easy to squeeze the shorts resulting in a rally of share prices, the opposite of what you want. A short squeeze doesn't change the fundamental or quantitative reasons you wanted to short. The technical analysis should only be used to help you decide your entry and exit price ranges amongst an otherwise random walk. The technical rules you created sound like something a very basic program or stock screener might be able to follow, but it doesn't tell you anything, you will have to do research in the company's public filings yourself. It is simply an average of what each analyst covering that stock are recommending, and since they usually only recommend Hold or Buy (rarely Sell), the value will float between Hold and Buy. Not very useful IMHO. Try Google Finance Screener ; you will be able to filter for NASDAQ and NYSE exchanges.