Here is something that I was just curious about given all the attention given to 40 yard dash times in football. Everyone agrees that speed matters in a receiver and below certain limits a player just won't get selected. To get a sense of how important it is I took a look at some data from NFL receptions leaders. A need trick if you are interested is to use the Excel : Data : Import External Data : New Web Query function built into the software. It will allow you to pull most tables of data off the internet with a few clicks of a mouse.
Here is a link to the source data I borrowed from ESPN's website (click here):
I organized the data into a spreadsheet and sorted it by receptions. Since I was also just interested in WR times I dropped the TE's from the list. Here is a link to the list in Google Docs reorganized as mentioned (click here for Google Docs Spreadsheet). The 40 times are collected off the internet and as such should be taken with a grain of salt. About one third are combine numbers, one third are from SI or ESPN or some other source, and 1/3 are just from search results from Googling names. The latter third in particular of course could be well off for all I know. For one receiver Bobby Engram I could not find a time so I accorded him with an average 4.55 time (I don't recall him being all that fleet of foot?). Some receivers like Joey Galloway and Torry Holt also note that I used their combine results (4.30 and 4.37) from years ago. If these times were somehow updated for older receivers like Galloway, Holt, Moss, or Owens, etc. it would be very likely that their times would be somewhat slower today. Anyway cut and paste the numbers from the Google Docs spreadsheet and adjust them if you have better data. This is all I could come up with in a short period of time using the internet.
So what does the shape of the curve look like for the leading WR's in the NFL? Below here is a histogram of the average 40 times that I could locate. As you can see below there are plenty of "speed burners" to the left and then a large spike around 4.50 to 4.55 in the middle. The mean time is an impressive 4.46 mark in the 40 yard dash. The one real data anomaly to the right is the reported Anquan Boldin 4.71 time from his disappointing combine performance a couple years ago. I am unfamiliar with the circumstances of that performance. He may have been injured, not trained for the event, or merely had a bad day for all I know.
I took it one step further for those interested and checked the r-squared values for the receptions with respect to 40 times, yards with respect to 40 times and average gain with respect to 40 times. There was not much correlation. Receptions to 40 yard dash time generated an r-squared of just .09 meaning it is not a very strong correlation at all (0 is no correlation, 1 = perfect correlation). Here is that plot for that data set below if you want to see the actual linear fit.
I would not make too many "conclusions" based upon that data. For one thing there are clearly different types of receivers in the league (Split end versus Flanker) and of course they can fall into categories like "possession" versus "deep threat" types as well. If someone had the time it might be more interesting to break the data into two different types according and do some deeper digging. I think it is also important to note that situational receivers like Devin Hester (more accurately a return man) can still have a huge impact on the game with only a couple touches per game even though he of course does not appear on the list as a top receiver. Still it is interesting to note that a significant number of players in the NFL (e.g. Wes Welker) put up very impressive numbers with no better than 4.55 speed. Technique and ability to get open are vital skills for any receiver regardless of speed. Plenty of "speed" guys have not done well in the NFL just as plenty of "slow" guys have struggled as well.
I checked the r-squared value for average yards per catch versus 40 yard dash time thinking it would show a better correlation. Faster guys should catch a few more deep balls I suspected. That value increased but only to about .21 so it was still not very high either. My guess as to why the r-squared for this simple comparison is low is that 40 to 50% of the passes in any given game are normally 3 step quick game routes (Screen, Hitch, Slant, Quick Out, etc.) or under 10 yards in length. Maybe 30% are 5 step drop patterns and the remainder are deeper or play action, or bootlegs, etc. Given that estimated distribution most passes are thrown of course for relatively short distances. Quickness in 10-15 yard range, the ability to burst and go deep, route precision, footwork, coverage recognition, technique, and ability to get off the line of scrimmage are probably better indicators of success for WR's? Those items are difficult to measure and compare which is probably why the NFL draft can look like a crap shoot with the benefit of 20/20 hindsight.
Regardless I still want a speed WR in the game for my team. Even if he does not catch a lot of passes a good deep threat still influence the overall pass coverage scheme and can sometimes open up space for underneath or intermediate routes for other wide receivers. That effect can only be verified by watching film and not reading numbers on a chart.