Because people hate being told about facts that directly contradict whatever fantasy they believe in.

Well VGChartz is has been consistently correct in the hardware figures if you compare them with the actual figures released by the hardware companies. This is the most reliable information, because these companies must provide correct information.
So if your friend wants the best information he should read the yearly and/or quarterly reports. All the numbers are in there.

VGChartz has also been very consistent with NPD, which has the largest tracking in the US.

If someone wants a source to prove Sony is still doing very bad, he should start his own site, because it's going better now, however I'd imagine there not close to where they want to be.

well, first off read the methodology page http://vgchartz.com/methodology.php

Here are some of my thoughts (note, I have a minor in math, but I'm no expert on statistics).

VGChartz, just like NPD, samples a portion of the market for sales information. Since they can't poll 100% of the market, they use statistics to "guess" how many were actually sold based on what their partners reported. Now I saw guess in quotes, because all VGChartz and NPD do is make educated guesses.

NPD has an advantage over VGChartz in that their sample size is considerable larger. This provides NPD with more safeguards that prevent them from having major mistakes in their results, however they are still possible.

While VGChartz has a smaller sample size, anyone with knowledge of statistics will tell you, that a small sample size with an excellent formula can be better than a large sample size with a poor formula. The downside of this smaller sample size is when an anomaly comes through their data, it is harder to figure things out, so their results can be skewed one way or the other easier. This is where you need good judgment on the part of the person compiling the data to determine if the final results look realistic.

One other difference, is that VGChartz doesn't fudge their new numbers if they get new information. Instead they go back and correct the week that was wrong. NPD may also provides corrections, but they do not provide any to the public.

NPD numbers for sell through tend to be pretty low compared to shipment numbers reported by Microsoft, Sony and Nintendo themselves, who are the only sources who know how much product (consoles or games) stores have bought.

npd is usa, vgchartz is north america, so you'll see numbers bigger for vgchartz.

Generally, in my experience here, you shoudln't take the software numbers very seriously, but the hardware numbers are usually pretty spot on.

Depends on if you have thousands and thosuands of dollars to spend.

Me i trust VGChartz over the monthly totals because we never get the NPD adjustments.

So if your looking for a grand total number it's better to go with VGchartz, then some hap hazard adding up every month NPD has given projection... or when a company quotes NPD numbers or seemingly do as they usually use PR means to make said things look different from what they are.

Well a few things first of all are that NPD is by no means absolutely correct. They too are using estimates based on the same statistical principles as VGC. Where they gain accuracy is in the use of larger data sets. But what any stats professor or student will tell you is that you don't need large sample sizes to have accurate data. A sample size of 50-100 would be sufficient to give accurate data about a population of tens of thousands. You can ask your friend to educate himself on estimation theory. You'll notice similarly that large political polling groups use sample size of about 3,000 to estimate for a population of 300 million people then I think you can begin to see where sample size is no problem.

You can also tell your friend that like every branch of statistics 100% precision is never gaurunteed and is not claimed by VGC in any way. Simply because a single console disagreed with NPD (which is simply another estimate anyways) does not mean that everything is wrong. What he is doing is called chery picking. He has found the data that fits his hypothesis and ignores all the data from the other months that don't support it.

Luckily devilstation recently compiled some numbers and you might find it interesting:

MARCH 08........................Wii...............PS3...............X360

VGC (-10% CAN)..............593,738.......318,254.......319,317

NPD...................................721,000........257,000........262,000

Sim Exchange.................. 593,000......301,000........296,000

Pachter............................700,000.......365,000........310,00

Other Months

JAN 08.............................Wii...............PS3...............X360

VGC (-10% CAN)..............286,946.......214,809.......236,357

NPD................................ 274,000.......269,000........230,000

Sim Exchange..................396,900.......209,300 ........288,600

Pachter..........................????????.......????????........????????

FEB 08.............................Wii...............PS3...............X360

VGC (-10% CAN)..............449,902.......299,606........295,569

NPD................................ 432,000.......280,800.........254,600

Sim Exchange.................. 400,700......269,900........249,200

Pachter...........................????????.......????????........????????

VGC VS NPD yearly Totals

Wii........1330,586.....Vs.....1427,000..... -96,414 .... (-3.50%)

PS3........832,669......Vs......806,800...... +25,869.... (+1.58%)

360........851,243......Vs......746,600..... +104,643.... (+6.55%)

You'll notice that despite one or two disagreeances for a specific console in a specific month the quarter comes out very close and NPD and VGC numbers actually agree. The big difference? VGC numbers are available weekly and are always out before NPD numbers.

There has been a lot of bitterness towards VGC especially from the pro-360 camp over the X-mas 2006 time frame when MS shipped a lot of hardware and VGC didn't represent it. The reason for this was VGC tracks point-of-sale or in other words sales to consumers, and MS had stuffed the supply chain to meet a stated Quarterly goal. So as a result of being at odds with the MS shipped numbers for several months (until the stuffed units eventually sold) many 360 supporters now bash the site, this is especially prevalent with the Neogaf forums which he unsurprisingly mentions specifically.

Either way, there are quite a few major gaming news and even national news outlets that use VGC and it is becoming more respected and recognized by the day. Perhaps in the past the data wasn't as wholly accurate as it could be but ioi and his team have strived over the past year and a half or so to make vast improvements to data tracking and estimation methods. Or in short, its getting better all the time, which is why VGC is more and more excepted.

Ultimately I posted this for you, as I really don't think your friend is going to hear anything of it.

Some people will just never accept VGChartz numbers as being accurate, their problem.

This seems most relevant to your specific discussion, which is about whether the PS3 or 360 is selling better this year. Through March, vgchartz and NPD are within a few percent of each other for all three home consoles. Both sources have the 360 and PS3 within 61,000 units of each other. Ironically (given your friend's preference for the 360), NPD has the PS3 selling slightly better than the 360, whereas vgchartz has the 360 selling slightly better than the PS3.

I'm going to put this short, since i'm too tired to look for my post about some of the reasons why some people tend to bash VGC (feel free to search my posting history, it should be there, a week or two ago in a similar topic, can't remember the name), but people use VGC bashing to diss the thing that is shown by all the other trackers too. Meaning that when someone says VGC is wrong, they actually say that everyone else is wrong too with their numbers, since the numbers, and especially trends, are supported by other trackers.
So, NPD tracks USA, VGC tracks the whole world, so i believe everyone should understand, that NPD can't be anywhere near as accurate as VGC.

VGC is the best and most accurate source available, when you see people summing up different trackers numbers at GAF, the numbers are far from up-to-date and there are a lot of regions where the data is missing (unlike VGC).

Oh, and in case someone says that we're saying this because we are VGC members; there's a reason why we are members on this site.