One well known study that indicated a potential anomaly in weak-form market
efficiency was Frank Cross' 1973 paper "The Behavior of Stock Prices on Fridays and Mondays".
In it Cross examines potentially non-random movements in the prices of stocks of the Standard
& Poor's Composite Stock Index. Cross acknowledges that "other researchers have found little
or no evidence of dependence in successive daily price changes. Apparently, however, these researchers have not investigated the possibility that dependence might occur on some days of
the week but not others" (Cross 1973). Cross examined a set of 844 Fridays and following
Mondays from 1953 through 1970. What Cross found was that on 523 (62%) of the Fridays, the
index advanced compared to only 333 (39.5%) of Mondays. He also found that when the index
advanced on Friday there was a 49% chance that there would be a further advance on the
following Monday. However, when the index declined on Friday there was only a 24% chance
the index would rise on the following Monday. Cross also investigated the relationship of price
patterns between other successive days of the trading week and found that no other pairs
displayed the same anomalous price patterns as Friday and Monday.