Dota 2 Item Timings

Defining the most important item timings

When we went to Captains Draft 4.0 in Washington DC, we spoke to Nahaz of datdota about the lack of good information out there on how much impact item timing has on winrate. Whilst many people who play DotA 2 have considered that there are items that could be more effective if purchased by a specific time, we have yet to see anyone attempt to quantify item timing in a meaningful enough way that we can make direct comparisons and rank times of purchase against one another.

Since we have detailed item purchase data on all heroes at STRATZ, we are in a good position to delve into this data and publish our findings.

When we asked the question, “By how much does winrate change for each minute the item timing is missed?”, we postulated that the faster the winrate falls off, the more important that item must be for attaining victory.

In mathematics, the slope or gradient of a line is a number that describes both the direction and the steepness of the line. Thus, the bigger the winrate-gradient for a hero-item combo, the more important it is.

In essence, we are equating item-timing importance with the rate of change of winrate, and expressing the rate of change as the mathematical gradient.

Let’s check out a sample winrate-over-time for Phantom Assassin Black King Bar purchases.

Phantom Assassin BKB. Blue points show win percentages of item purchases in that minute [error bars indicate 95% confidence interval, calculated by assuming win-loss can be represented by Bernoulli trials]. Orange line represents the distribution of when item was purchased. The dashed lines indicate the times between which approximately 69% of the results lie. Solid lines indicate the mean purchase time of the item on the hero (vertical), as well as hero average winrate (horizontal).

This winrate shape is similar to what we see for many hero-item combos. Unpredictable behaviour often occurs very early and very late.

This unpredictability can be attributed to a combination of fewer games where purchases were made at odd times, and a higher proportion of ‘weird’ item build orders. As an example, some very early timings on items occur when players skip boots and other important early game items to rush their first big item out. This tactic is effective in far fewer situations than it is attempted.

Note that in the central 69% of timings (purchases between 1 standard deviation above or below the average purchase timing), we tend to get a sensible well defined slope. In other words, the winrate decreases every minute the item gets delayed. Therefore, we define our winrate gradient as being the [linear] gradient in the area between these 69% boundary times.

For some of these graphs you will notice that any purchase time for an item has a higher winrate than average hero winrate. How is this possible? Simply completing an important item can be crucial to winning. If the game ends before a hero can finish building their item, there is a very high probability that they lost the game.

How do different build orders affect results?

Why could this be a problem? We will use two examples:

a) Armlet on Huskar

b) Orchid on Storm Spirit

a) Huskar Armlet (Averages: 49.2% winrate, 13min 25s timing)

b) Storm Spirit Orchid (Averages: 49.2% winrate, 27min 31s timing)

In our first example, armlet on Huskar is an essential first major item for two reasons:

Huskar’s passive gives magic resistance, so he only requires armour and HP to survive, both of which are provided by armlet.

Huskar’s passive increases his attack speed as his health decreases, so the ideal situation is to maintain low enough HP to deal tonnes of damage while avoiding death. Since armlet can be toggled to control his HP, it’s arguably the perfect item.

This is why armlet is purchased in over 98% of Huskar games at Divine level.

In our second example, Orchid is a great item on Storm because the hero requires mana regen and attack speed, both of which are provided by Orchid.

Storm Spirit players will sometimes go Orchid straight after boots, especially against enemy cores with important escape spells like Puck or Ember Spirit. However, seeing Storm attempting to build Orchid will trigger either Euls Scepter, BKB or Manta Style purchases to dispel the Orchid silence. This is a situation where poor timing can greatly decrease Orchid’s usefulness against those cores. Since kills on supports aren’t as valuable in the early stages of the game, the Orchid rush becomes very detrimental.

Due to this risk, many Storm Spirit players will opt for items that don’t offer as much kill potential but increase their farm speed significantly, like Bloodstone or Kaya, and purchase Orchid later on. We have already explained that it is a great item on Storm in general, and can assist in late game pickoffs on defenseless supports; a more useful objective when the game is 5v4.

In a case like this, an item build that delays purchase may have a winrate as high or higher than builds that rush the item.

This presents an issue where we are not 100% sure if a 25 minute Orchid purchase is a really poor timing on a rushed Orchid or a really good timing on a delayed Orchid.

These conflicting factors should naturally lead to shallower slopes or more weirdly shaped graphs in general. The timings will be more spread out as possible build variation increases.

Therefore a) will naturally have a bigger winrate gradient than b) due to greater item build variation.

Does this invalidate our approach for defining ‘most important item timings’? We don’t believe so. Why?

If an item can be purchased at multiple points in response to different circumstances, then it is inherently less important for a hero than an item that MUST always be purchased at a specific point.