Hi Mohamed,

Michael Marek recently raised a question in RG regarding the Hawthorne effect-i.e. temporary increases in a research subject's performance, owing to the effect of being observed. I suggest  you look at his question and some of the answers for ideas:"Do research studies need to address the Hawthorne Effect?" . There is also quite an extensive literature on this subject ( which I knew nothing about prior to reading Michael's question) so you might want to read more widely on it, especially to see if there is any evidence or, at least, intersubjective consensus on the timescale needed to overcome this effect. A good starting point could be: J Clin Epidemiol. 2014 Mar; 67(3): 267–277.

doi:  10.1016/j.jclinepi.2013.08.015

PMCID: PMC3969247

Systematic review of the Hawthorne effect: New concepts are needed to study research participation effects

With regard to collocation, I would opt for as long a period as is expedient for you, in order to:  look for long-term gains in learners collocational awareness and see if learners begin to link taught collocations/collocational groups to semantically associated collocations or collocational groups which have not been taught;  see if it can lead to long-term improvement in the use of grammatical structures, in line with what is claimed by Pawley and Syder or Nattinger and De Carrico, among others; see if the teaching of collocation can bring about changes in students' approach to any of the four macro skills or to the way that they learn English in class and at home-e.g in dictionary use. Most importantly, you would need to be satisfied that any observed effects that relate to your main research questions have finally stabilized. Larsen Freeman and Cameron's complex systems approach-Complex Systems and Applied Linguistics (OUP) -is relevant here for understanding how change in language competence and performance takes place. A quick reexamination of this book suggests that chapters 3 , 5, 7 and 8 are likely to be the most relevant.

If you cannot carry out a very long -term initial study, you could plan a follow-up study .

Dear Chris , thank you for this sobering advice . As for the duration of my classroom experiment , you are absolutely right . Long-term classroom investigation is really revealing of my study  subjects perception , processing and , more importantly , producation of lexical collocations . Getting research participants exposed enough can ensure the acquisition of collocations . 'Attention enhances retention" ( Shmidt , 1991 ) . Every class i give , targeting collocations found in the  given text , reveals alot about those learners processing of collocations . But what i need to ensure more is that by the end of the planned duration of the experiment , the subjects will have the habit  of using collocations ( operating on the idiom principle ' Sinclair 1991" ) ingrained without the need for recycling the teacher 's taught collocations .i,e , operating on the idiom principle as a natural language behaviour in L2 as they do in L1 currently