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Since I started using the Dvorak layout a couple of years ago, my interest for different keyboard layouts has increased significantly. I have tried out Colemak as well, although I never reached a high speed with it, but at that point I felt that I personally preferred the Dvorak layout. My favorite feature with Dvorak is the high degree of hand alteration, and in particular that all the vowels are on the left-hand side, while the common consonants are on the right-hand side. After having gotten used to that, I didn't want to give it up. Therefore, I started to think about ways that the Dvorak layout could be modified, to get a better Dvorak-like layout, while maintaining the feature I like with Dvorak. I looked at several other popular layouts for inspiration, and tried out different modifications, guided by letter and bigram frequencies, to minimize consecutive finger use and trying to make the most common bigrams comfortable to type. After a lot of thought and testing, this resulted in the AHEI layout (named after the home row). It performs better than several popular and optimized layouts (including the Dvorak and Colemak layouts) according to two different keyboard layout analyzers. The most common letters are easy to reach from the home position, and common two-letter combinations are rarely typed with the same finger.
The layout should be easy to learn if you already are a Dvorak typist, since Dvorak was the starting point. 11 letters have the same positions as on Dvorak, and most of the other letters are close to where they are positioned on a Dvorak keyboard. Only two letters, H and Q, switch sides. The layout solves the Dvorak issue of having to stretch for the common letter I, while maintaining comfortable typing of the common bigram OU. It also decreases the load on the right pinky finger, and removes the moderately frequent letter F from its unfavourable position on the Dvorak keyboard. After having used this layout for about half a year, I am still quite satisfied with it (although I of course, every now and then, think about how it could be further improved). So I wanted to share it, including my thoughts and insights gained while working with it, in case some of it could be interesting to someone else.
Image of the layout, including some performance indicators: The AHEI layout
When looking at the letter frequency heat map for the Dvorak keyboard, it seems that the most obvious improvement would be to switch I and U, since I is a much more frequent letter, and thus should be placed at one of the eight home keys, that don't require any stretch or lateral movement. An argument for not doing this is that OU is the most common vowel bigram, and this would be less comfortable to type if I and U were switched. The second most common criticism against the Dvorak keyboard is that it puts too much effort on the weak right pinky finger, which is assigned to two common letters: S and L.
For the most popular alternative keyboard layouts, Dvorak and Colemak, it seems like the keys on the home row — including the keys in the middle columns — are viewed as the best positions. Some people argue that the lateral movement to reach the middle column requires more effort than moving some fingers up and down, and that the middle columns thus should be de-emphasized. This approach has been taken for many newer layouts, such as the Workman layout and the Colemak Mod-DH layout. Some computer-optimized layouts such as the MTGAP layout and the very recent Engram layout even avoid putting letters at all in the middle columns, and use some or all of those keys for punctuation marks.
I have tried to use ideas from these different layouts it order modify the Dvorak layout and improve it. I want to keep the high degree of hand alteration, which is a feature I like with Dvorak, and therefore I want to keep all the vowels on the left-hand side, and most of the common consonants on the right-hand side. I also prefer to keep the keys close to their positions on Dvorak, since that's what I'm used to, and it would thus be easier to learn the new layout. The main objective is to find a design such that all common bigrams (two-letter combinations) are comfortable to type. We would for example like to avoid having to type common bigrams with the same finger.
The best keys are obviously the eight home keys, so we would like to place some of the most common letters there. Personally, I think that the second best keys are the ones above the middle and ring fingers, and the third best are probably above or under the index finger. The reason that the keys above the index fingers aren't included in the second category is that I find them slightly harder to reach on a classical keyboard, when I have my hands slightly angled, for a more ergonomic wrist position. So, on the 12 best (in my opinion) keys, I would like to fit most of the common letters.
One solution for the U-I problem, that is used in both the MTGAP and the Engram layout, is to place O above the E key, and U next to it. In this way, we can both fit the common letter I among the home keys, and at the same time type the common bigram OU comfortably, while keeping O at one of the second best keys. The second most common vowel bigram IO is also comfortable to type with this solution (more so than on Dvorak, where it requires a stretch). This leaves us with one free spot among the left-hand home keys. Since there are more common consonants than good positions on the right-hand side, it would make sense to move one of the consonants to the now free good spot on the left-hand side. The most common English bigram is TH, which, I assume, is why these letters are placed next to each other on Dvorak. However, after TH, we usually have a vowel, and most commonly E. HE is the second most common bigram. Thus, one idea is to move H to the left-hand side, so that combinations with E and other vowels are easy to type. Putting H on the old O-spot gives HE a nice inward roll, and HA, HO and HI are also nice and easy to type. At the same time, we have freed up one of the good spots on the right-hand side, so that we have more room among the good keys there for the common consonants.
The next step is to rearrange the consonants on the right-hand side so that the most frequent ones are on the best keys, while avoiding that common bigrams are typed with the same finger (i.e. keeping consecutive finger use low). After having tried out many options, I ended up with the result in the linked image. The 11 most common letters, ETAOINSHRDL, all have a frequency above 4%, while the rest of the letters have a frequency of less than 3%. All these letters are now fitted into the 12 best positions on the keyboard.
One of the worst positions on a standard staggered keyboard, among the letter keys, is probably the Dvorak F position (QWERTY Y), since it requires a long stretch. Therefore, I also made sure to remove the quite common letter F (2.2%) from there, and replace it with the second least common letter Q (0.1%). Also note that the finger assignments on the left-hand bottom row are displaced one step to the left, in accordance with the angle mod used for the Colemak Mod-DH layout, for a more ergonomic typing posture. The J has been moved away one step further from K, compared to Dvorak, to avoid having to type bigrams with J and a vowel with the same finger. I also incorporated the brilliant idea from Colmak of turning the caps lock key into a backspace key.
To evaluate the layout, I mainly used the keyboard layout analyzer http://patorjk.com/keyboard-layout-analyzer. The new layout scores higher than all the ones that I have compared with, including Dvorak, Colemak, MTGAP and the newest Engram layout, for all of the three provided sample texts. These include the first chapter of Alice in Wonderland (results shown in the image), a list of the most commonly used words, and a list of most commonly used SAT words. The alteration between the hands for the first text is almost identical to the result for Dvorak, while it is significantly lower for Colemak, and slightly lower for the MTGAP and Engram layouts.
Also with the analyzer https://colemakmods.github.io/mod-dh/analyze.html (where a low score is better), it gets a better score (1.77) than Dvorak (1.92), Colemak (1.84) and MTGAP (1.79). This analyzer uses a corpus with books from Project Gutenberg for evaluation (the same as used by the carpalx optimizer). The result here also shows that the AHEI layout is better at avoiding frequent same-finger bigrams than the Dvorak layout (which is seen by the first analyzer as well, by the diagram included in the image). The most common same-finger letter bigrams for Dvorak are GH (0.34%), CT 0.20%, RN (0.16%) and UP (0.16%). For the new layout, the top list instead consists of KI (0.13%), RM (0.10%), UI (0.10%), SC (0.10%), of which KI and UI are present in the Dvorak layout as well. Furthermore, the distribution between the hands is a bit more even for AHEI (left 51.2%, right 48.8%), compared to Dvorak (left 45.3%, right 54.7%).
Finally, I also made a Swedish version of the layout, since I type a lot in Swedish as well. Like the SvDvorak layout, I have kept most of the non-letter keys as in the Swedish QWERTY layout, and added the three extra letters in the Swedish alphabet. Trying it out with the first analyzer, using some news articles in Swedish, it also outperforms SvDvorak and a Swedish Colemak variant (and, needless to say, the Swedish QWERTY layout).
After having given a lot of thought to this, and reaching a result that seems rather satisfying, I wanted to share my thoughts and results, in case that it could benefit someone else as well. It would be fun if someone else either wanted to try it out, or could use the ideas to construct a layout that suits them.