Odd Lot Theory
In technical analysis, the theory that odd-lotters (defined as small investors who deal in fewer than 100 shares at a time) are both badly informed and have low risk tolerance. Therefore, an investor may profit by doing the opposite of whatever odd-lotters are doing. For example, if a technical analyst sees that a substantial numbers of odd-lotters are selling a particular security, he/she may take this as an indicator to buy that security. The theory had some prominence in the 1960s and 1970s, but came under criticism later for lack of evidence that odd-lotters' investments underperformed the market as a whole. By the 1990s, the odd-lot theory had largely fallen into disuse, in part because of the growing popularity of mutual funds for small investors.
The technical theory that holds that an investor should make investment decisions contrary to what the odd-lotters, on balance, are doing. For example, if odd-lot sales exceed odd-lot purchases, the odd-lot theory says that the smart investor should buy. Conversely, if odd-lot purchases exceed odd-lot sales, the theory says that the smart investor should sell. The odd-lot theory is based on the premise that small investors who trade in odd lots tend to make the wrong decisions.