[cubeguy314]

So a lot of you know about the armor enchantments Protection 4 and Protection 3, and I'm sure many of you have heard the rumor that Protection 3 provides equal protection as Protection 4 (as stated in one of N2Z's posts). I have tested this rumor using the scientific method using multiple and repeated trials.

Spoiler:

From the data I have obtained, I have concluded that Protection 3 will protect you as well as Protection 4 will with only very insignificant differences in damage taken over a long period of time--much longer than a PvP fight.
Observations: In addition, Protection 4 seems to have used more armor durability (I didn't test too much on this). When dealt 2 hearts of damage with a Sharp V sword upon a Protection 4 chest plate, the chest plate lost 2 units in durability; whereas, a Protection 3 chest plate, when dealt 2.5 hearts of damage, lost 2 units in durability.

Of course, this is the average of the results because due to Minecraft's range of damage inflicted upon a single strike, health damage received will vary (equally).
Furthermore, it costs more experience to repair a Protection 4 chestplate than it does to repair a Protection 3 chestplate of equal durability.

Conclusion of experiment: In the majority of situations, a Protection 3 chestplate can serve equal protection as a Protection 4 chestplate will, and a Protection 3 chestplate is also better financially.

If anyone would like to perform this experiment and determine for themselves whether or not I'm correct, here is the experimental design.

Spoiler:

The experiment design consisted of 2 testing zones for each chestplate: "Damage from an arrow shot from a dispenser" test, and "Zombie with Sharp V sword" test. Each test zone consisted of 2 individual tests that were repeated due to the varying ranges of damage that can be dealt. Tests consisted of the "Health Damage received" test and the "Armor Damage received in proportion to Health Damage received" test.

[mr. roach]

Well done. Thanks for the info!

[OneManWo1fPac]

Give me some iron and a wood sword and send me in coach, that'll do the job

[Nephalem]

Great info, you should make some more "Minecraft Myth Busters"!

However:
- It doesn't matter if I wear protection 3 or 4, cactus still beats me in 1 vs 1.

[Cephyrian]

Roach doesnt care, he will still kill you in a matter of seconds...

[FrostyBirth]

Well, this was true prior to 1.5.2/1.6. Now, Protection IV is the better armour. The EPF (Enchantment Protection Factor) has been altered in a way where neither will fully protect you anymore.

These are the new EPF's as of 1.6.2:

The maximum you may receive is 25. Protection IV gives a max of 20, while Protection III is only at 12.

I have concluded that Protection 3 will protect you as well as Protection 4 will with only very insignificant differences in damage taken over a long period of time--much longer than a PvP fight.

Fights can actually last quite some time. That "insignificant" difference could be the difference between dying, or staying alive.

Basically, if you're going to be fighting/getting attacked , Protection IV would suit you better, even if your fight is short.

[cubeguy314]

The maximum you may receive is 25. Protection IV gives a max of 20, while Protection III is only at 12

Maximum what? What are your numbers' units and their ratio to damage received?
Furtthermore, attacks don't have fixed ratios. Just because your diamond sword says +7 attack damage doesn't mean it will deal 7 damage all the time (to a normal mob). I'm referring to the possibility of variances with attack damage.

[FrostyBirth]

The EPF. I will have to see if I still have the equation when I get home, but it determines how much damage will be protected by your armour. Since Protection IV has a higher EPF, more damage will be reduced than a set of Protection III.
I'll be able to explain more once I'm home.