Overall problem: relationship to 'time'
i) longitudinal (following the same learners from Time 1 to Time N)
ii) cross-sectional (taking a sample usually of dfifferent people at Time 1, Time 2, Time N and comparing)
iii) experimental time (i.e. ultra short-term 'learning' in experiments etc)

General methods
the observational method - language elicitation and analysis e.g. Hatch
the difference method - measurement of learner or situational variables and correlation with proficiency or something else
the manipulative method - treat one group, not the other, measure effects of treatment

Types of evidence
i) introspection: thinking aloud, self-observation, grammaticality    judgements
ii) natural data; e.g. Faerch, etc
iii) controlled data

Ethical constraints on experimenters

Designing an L2 research project ('problem decomposition')

1. Is speech more important than writing?

2. Is speech more important than writing in L2 learning?

3. Is speech more important than writing in the L2 learning of
vocabulary?

4. Is speech more important than writing in the L2 learning of English vocabulary by French adult learners?

6. Is a group of French adult learners of English in technical schools in France which is taught orally better at learning vocabulary than an otherwise identical group that is taught through writing?

7. Are the scores on the EPVT of a group of French adult learners of English in technical schools in France who are taught orally better than an otherwise identical group that are taught through writing?

8. Are the scores on the EPVT of a group of French adult learners of English in technical schools in France who are taught orally
significantly better than an otherwise identical group that are taught through writing?

A fuller explanation of this sequence will be found in Chapter 1 of V.J. Cook (ed.), Experimental Approaches to L2 Acquisition, Pergamon, 1986.