Evidence that learning radicals speeds up character learning in Chinese?

Question

Characters — in Chinese or Japanese (or Korean Hanja) — can be learnt in various ways, and it is plausible that paying attention to radicals helps memorisation and retention. But is there any hard evidence for this?

Are there any studies on the effectiveness of character learning or teaching methods that pay attention to semantic radicals? (By "semantic radicals", I mean those that carry meaning, as opposed to phonetic parts or even single strokes that are used in dictionaries for lookup purposes.)

PS: Wikipedia has a few lists and articles that are related to radicals:

• Radical (Chinese characters); see also the corresponding entriy in the Chinese version of Wikipedia: 部首 (bù​shǒu).
• Table of Indexing Chinese Character Components: by stroke order.
• Table of Kangxi radicals.

PPS:

• On Chinese SE, someone asked in June 2014 whether memorising 214 Chinese characters was avoidable.

Answer 1

The 1999 article "Using Radicals in Teaching Chinese Characters to Second Language Learners" by Marcus Tuft and Kevin Chung reported on a study where students who new nothing about the Chinese writing system ("naive learners") were taught 24 Chinese characters (each composed of 2 radicals from a set of 16 radicals) under the following conditions:

1. Radicals Before: students were told about radicals and given 15 minutes to learn the 16 radicals before seeing the actual characters.
2. Radicals Early: students were told about radicals when they first saw the characters and were asked to identify the radicals in each character on a chart.
3. Radicals Late: students were told about radicals only at the third and last session and were asked to identify the radicals in each character on a chart.
4. No Radicals: students were not told about radicals; this was a control group.

Each group was tested twice: a first time just after the third and last learning session, and a second time one week later.

When ordered by correct test results (both for the first and the second test), the groups were:

1. Radicals Early
2. Radicals Before
3. Radicals Late
4. No Radicals

The Radicals Early group scored significantly better than the other groups in the first test. The differences were smaller in the second test; according to the researchers,

Presumably, this was because the maximal level of performance was so reduced after a week's delay that the sensitivity of the different learning conditions was lost to a floor effect.

The researchers concluded that the experiment indicated that "knowledge about radicals is something that facilitates the learning of characters that contain those radicals."

Answer 2

Let me add a couple of thoughts. I'm posting them here, as they are too long for a comment.

A good SLA study should not only provide empirical results, but also a model that explains them. The results of the study you quoted are uncontroversial, and I'm pretty sure they could be reproduced. But that doesn't solve the question of the usefulness of radicals in Chinese character pedagogy. The problem I see here is that radicals (in the sense of 部首) cannot be considered a psychologically realistic category. Learning radicals does seem to speed up learning, but most likely it does it because, accidentally, they partially overlap with some useful category, such as semantic components or phonetic components.

Different radicals belong to different categories:

• some radicals are arbitrarily chosen semantic components¹,
• some radicals are phonetic components²,
• some radicals are graphical components (without any clear phonetic or semantic value),
• some radicals are strokes³.

At least some of these categories are likely to be psychologically realistic and learning them probably speeds up character learning. But radicals make up an arbitrarily chosen set of components and strokes:

• some strokes are radicals (e.g. 丨,丿) and some are not (乀),
• some phonetic components are radicals (臼) and some are not (e.g. 甫),
• some semantic components are radicals (e.g. 言 in 話) and some are not (e.g. 正 in 歪). The list can go on and on.

Radicals are really nothing more than an indexing tool for looking up characters; after all, the name 部首 simply means ‘section headers’ (in Xu Shen's Shuowen Jiezi dictionary).

If we were to believe that radicals are an important learning tool, by the very fact that they are radicals, teaching of 讓 should be focused on the radical 言. But it's quite clear that the part that causes most trouble is the component 襄. Similarly, correct recognition of the non-radical 甫 is probably a greater problem than the recognition of the radical 勹 in 匍. And the fact that 止 is the radical of 歪 ‘crooked’ isn't going to help with learning that character. What is needed is the recognition of its two semantic components: 不 ‘not’ and 正 ‘straight’.

My conclusion: it'd be much more useful to ask whether learning semantic components/phonetic components/graphical components/individual strokes can speed up learning the characters. I don't have answers to all these questions, but I have hypotheses about some of them. Sets of radicals that are used for indexing dictionaries is a mixed bag of arbitrarily chosen members of the above groups, and is therefore far from the optimal set that should be learned in advance. But I must admit that learning radicals is probably still better than learning characters without paying any attention to their structure at all.

<sub>1. e.g. the radical of 尖 ‘pointed’ is 小 ‘small’, but there is no reason why it shouldn't be 大 ‘big’; both components clearly have a semantic function here
2. e.g. in Shuowen Jiezi, 几 is said to be the radical of 鳧 and is indicated as a phonetic component; in modern radical systems, 臼 is both the radical and the phonetic component of 舅, etc.
3. e.g. 丿 is the radical of 乖, but it can't be really called a component: the most sensible decomposition of 乖 is 千 + 北, and 乖 without 丿 is not a component</sub>