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KhatzuMemo Update: Repetition Scheduling Algorithm

Peace in our time! KhatzuMemo has been updated.

It’s not a pretty, user-interface update, it’s in the nuts and bolts behind the scenes. The repetition scheduling algorithm on KhatzuMemo has been modified to take into account more of the extensive data that get collected with each repetition of an item. I’d found that there was a problem whereby repetition scheduling on some items was prematurely optimistic — over-extension of interval. Now the interval is normalized, taking into account cumulative score, mean score and lapse ratio for a single item.

Anyway, the executive summary is — it’s the best KhatzuMemo repetition scheduling yet. I’m very proud of it and you should see a steady rise in your retention rate because of it.

  23 comments for “KhatzuMemo Update: Repetition Scheduling Algorithm

  1. Elliott
    December 6, 2007 at 18:54

    Your website is really interesting for me as I’ve spent a couple of years doing evening classes in Japanese and don’t feel I’m progressing fast enough.
    I attempted to use KhatzuMemo, but it keeps asking me the same question all the time.
    I uploaded update 30 questions, but irrespective of which number I select the same question appears!
    Are you still updating the app?


  2. khatzumoto
    December 6, 2007 at 19:12

    >irrespective of which number I select the same question appears!
    Give the item a higher score (higher number = higher score; 5 is the highest), assuming the item deserves it, which it probably does at this point…

  3. JDog
    December 7, 2007 at 05:05


    Since Christmas season is underway and I shouldn’t be listening to English music now, I was wondering if there is a such thing as Japanese Christmas music. I don’t really know what I’m talking about because I don’t know how they celebrate it (or if). If there is, it seems like the songs would be easy to learn because I already know all the words so well to the English songs (if they’re translated).

    Have a good one,


  4. quendidil
    December 8, 2007 at 00:05

    Khatz, this might sound a bit odd, but is the Japanese “The Sound of Music” COMPLETELY dubbed in Japanese? Although over on Amazon they list the languages as 英語, 日本語 but I wonder if the songs are also dubbed in Japanese. The same goes for other musical-shows like My Fair Lady.

    JDog, I think Christmas in Japan is primarily thought of as a lovers’ holiday and not one for the family. If it’s spent at home, people just laze about at home. There is a trend towards spending Christmas with the family though, at least according to wiki.

  5. scout
    December 8, 2007 at 02:31

    I’ve come across two problems with KhatzuMemo and so far I’ve been unable to resolve either one on my own. Hopefully someone else will be able to clue me in as to what I’m doing wrong.

    1) I’ve been trying to use KhatzuMemo from a computer with both Firefox 2 and IE 7. I’m currently unable to get past the first question. After I look at the answer and rate how easy it was, the second rep shows the exact same question. Worse yet, the number of reps for the day goes up by one each time I do this. This seems to go one forever. (Admittedly, I’ve only actually tried it ~5 times in a row before giving up.)

    2) It seems like my cell phone (a Verizon LG VX8300) doesn’t want to play nicely with KhatzuMemo — the login page works, but after logging in I get a blank page. I originally wrote off using my cell phone since it lacks support for Japanese text, but now that it can be displayed as an image I’m trying to figure out what’s giving it issues. Has anyone else seen something similar?


  6. Deven
    December 8, 2007 at 10:08

    scout, I’ve been having the same problem as you with you #1.
    number 2 I’m not entirely sure don’t have that phone, or Verizon for that matter.

  7. Deven
    December 8, 2007 at 12:33

    Oh, one more question for Khatzumoto.

    would it be possible to add a function to khatzumemo where, you can have multiple categories in the review section?

    like a section for Words and a section for Sentences(you could make whatever categories you needed though.) but I don’t only SRS sentences I’d also like to SRS words that I keep forgetting and need to remember, but would like them in their own category.

  8. December 9, 2007 at 02:08

    Hey JDog, Chara’s got a new single out in the spirit of xmas: 僕のことを知って

  9. JDog
    December 9, 2007 at 10:59

    OK, thanks ruisu! I’ll have to check that out.

  10. khatzumoto
    December 9, 2007 at 19:55

    You mean, like splitting things into different categories/sets instead of having it all combined?

  11. khatzumoto
    December 9, 2007 at 19:59

    #1) I made the scheduling stricter so that you have to really LOOK at the item and THINK about how you’re going to remember it somewhat, and essentially earn yourself a 5-point score (maybe more than one)…that should only happen with new items or items with a bad track record. The reason for this is that when a lot of people “forget” something, usually it’s because they never GOT it in the first place. I was wanting this to make you really think “are ya sure you know this? really?”…

    If you find that too strict I might change it, or make it so that that item comes up later on that same day.

    #2) I have seen that error…do you have cookies enabled on your cellphone web browser? Try that. Let me know if it still doesn’t work…

  12. khatzumoto
    December 9, 2007 at 20:02

    1) I’m going to take a trip to my video store JUST for you, dude…JUST for you. Let me put it on my date list. I’m going to rent the movie at IMMENSE personal cost and go through that noss to see whether the songs are in Japanese 8)
    [General pattern: original music for the movie is often dubbed, especially if sung by characters…in any case I will check and report within 3 weeks]

  13. khatzumoto
    December 9, 2007 at 20:11

    The Internets gave me this list (chart) of Christmas singles. The format is [SONG ARTIST].
    I googled: クリスマスソング 邦楽
    i.e. Japanese Christmas music.

    You might be able to play some for free from here:
    Gyao is free and only requires registration…I think you can even give fake email oops did I say that out loud.

    1位  クリスマス・イブ(山下達郎)
    2位  すてきなホリディ(竹内まりや)
    3位  恋人がサンタクロース(松任谷由美)
    4位  メリクリ BoA
    5位  appears/CAROLS 浜崎あゆみ
    6位  星屑の街 ゴスペラーズ
    7位  WINTERS SONG  ドリームズ・カム・トゥルー
    8位  白い恋人達 桑田佳祐
    9位  いつかのメリークリスマス B’z
    10位 クリスマスイブRap キック・ザ・カンクルー
    11位  雪が降る街 ユニコーン
    12位  クリスマス JUDY AND MARY
    13位  サイレントイヴ 辛島美登里
    14位  聖なる鐘がひびく夜 タンポポ
    15位  聖者が街にやってくる Laughin’Nose
    16位  Dreams of Christmas TM NETWORK
    17位  クリスマスキャロルの頃に 稲垣潤一
    18位  雪のクリスマス DREAMS COME trUE
    19位  クリスマスなんて大嫌い!!なんちゃって クレイジーケンバンド
    20位  白いクリスマス JUN SKY WALKER(S)
    21位  HERO Mr.Children
    22位  雪に願いを 槇原敬之
    23位  White Love Speed
    24位  Dear…again 広瀬香美
    25位  クリスマスラブ サザンオールスターズ

  14. khatzumoto
    December 9, 2007 at 20:45

    Also try selecting “Remember me” on your cellphone, when you login.

  15. Deven
    December 10, 2007 at 03:31

    yes that is what I mean, allow different categories.

    that way I could have my words and sentences separate.
    and I could add things for school classes if I needed to as well without having them mixed in with all the japanese

  16. scout
    December 10, 2007 at 05:12

    Khatz, Thanks for your suggestions. It does seem that I wasn’t spending long enough looking at the answer — if I pause 10 seconds or so, it seems to move on to the next question. I think the problem is that the amount of time it takes to read and ‘get’ a rep is highly dependent on the card contents. The one I was never getting off of was an old, simple question that immediately made sense to me. (I had imported some old questions from another SRS.)

    I’ve tried enabling ‘remember me’, but it doesn’t seem to change the phone’s behavior. It looks like it gets stuck on login.php, and never moves off of it. I wonder if the phone refuses to allow automatic forwarding to the next page?

    Sadly it looks like Gyao is restricted to those with Japanese IP addresses. Whenever I go to register, it tells me it’s limited to use in Japan. (I even tried using a email address, but that didn’t seem to help.)

    Thanks again for your help!

  17. khatzumoto
    December 10, 2007 at 09:22

    I’ve been thinking about that. Thank you for the suggestion. I will add it to the feature list. It may take a little while, but that’s a really good idea and I’d like to implement it. Thanks again.

  18. khatzumoto
    December 10, 2007 at 09:24

    Yeah, redirection may be the problem. In that case, I think I can fix it quite easily by adding a manual link…

  19. khatzumoto
    December 10, 2007 at 09:27

    Is there a “enable redirection”-like option on your phone’s browser settings?

  20. scout
    December 10, 2007 at 10:19

    Unfortunately I haven’t been able to find such an option. (I also did a quick Google search, and haven’t found anything useful.)

    Just for kicks, I had the phone navigate directly to question.php after I tried to login. I got the same thing — a blank page. The odd thing is the blank pages I’m seeing don’t look entirely empty — there is a scroll bar to the right, but the phone won’t let me scroll around at all. (It just beeps when I try to move down.)

  21. Deven
    December 10, 2007 at 15:13

    thank god for Khatzumoto!

    wow thank you soo much!!
    I’ve been using your SRS (khatzumemo) for like a week now and I’ve been thinking it wasn’t working, but all the sudden, I see myself pressing 4’s and 5’s over and over again now!

    I never even knew I could remember this well!
    so thank you khatzumoto! you developed the SRS I’m using and you’re the one who first introduced me to the idea of an SRS so I have to thank you for that, and I couldn’t think of a better place to put this so.. thanks

  22. quendidil
    December 11, 2007 at 01:07

    Wow, thanks a lot really! *hugs* 🙂

  23. Prom
    December 18, 2007 at 17:01


    I wonder why the sentences which I’m bad at (and thus get a low score) show up immediately again. Wouldn’t it be better to add them again to the end of the current days stack? So maybe the last item of the day would be asked again and again, but not all of the items i fail once. It’s pretty easy to remember them when they show up immediately again.

    Btw. what’s about the mobile version… hard to figure out a solution?

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