:Nonetheless, Lafem asked me for a definition in a common dictionary. I have found a lot, but I cite those in Internet:  

 The demanded definitions of over-representation  

 :All those are in on line dictionaries. The first one redirect you to some of the others  
 :::http://www.onelook.com/?w=overrepresented&ls;=a 
 :One of the others is the Merriam Webster dictionary:  

 :::http://dictionary.reference.com/search?q=overrepresented 
 :::http://www.m-w.com/dictionary/overrepresented 
 :::http://www.bartleby.com/61/3/O0190300.html 

 :The Oxford English Dictionary is maybe a too technical one. It is made for philologists. However, I think this is authoritative enough. Some of the article's entries on "Over":  

 :::    27. a. With verbs (both transitive and intransitive), and with nouns or adjectives used as verbs. Many verbs arose in Middle English; those treated as main entries include OVERCARK v., OVERCHARGE v., OVERDRIVE v., OVERHEAT v., OVERLADE v., OVERPRAISE v. In the 16th cent. such formations began to abound, as OVERBLOW v.1, OVERBOIL v., OVERBURDEN v., OVER-BUSY v., OVERCLOY v., OVER-CRAM v., OVERDARE v., OVEREAT v., OVER-FEAR v., OVERGORGE v., OVER-LABOUR v., OVERLOAD v., OVER-LOVE v., OVERREACH v., OVER-ROAST v., etc. Some of the occasional formations listed below date from before 1600 (and a few from before 1500); after 1600 it was effectively possible to prefix over- in this sense to any verb whose sense allowed it. over-accentuate, -afflict, -agonize, -answer, -argue, -assess, -bake, -black, -blame, -boast, -borrow, -brown, -brush, -characterize, -cherish, -chill, -cleave, -coach, -commend, -commit, -complicate, -concentrate, -condense, -confute, -control, -creed, -cull, -cultivate, -damn, -decorate, -deflate, -digest, -dilute, -discipline, -discount, -doctrinize, -doze, -dramatize, -dread, -dull, -edit, -elaborate, -emphasize, -engage, -enjoy, -enrich, -exact, -exaggerate, -exalt, -expect, -explain, -fag, -fancy, -fatten, -fee, -feel, -fix, -flatten, -flog, -force, -furnish, -gamble, -goad, -grace, -grasp, -gratify, -gun, -handicap, -harass, -hate, -help, -honour, -horse, -humanize, -hurry, -import, -ink, -instruct, -interpret, -invest, -involve, -itch, -job, -laud, -linger, -list, -loathe, -magnify, -marl, -meddle, -mix, -moisten, -mortgage, -multiply, -nourish, -nurse, -objectify, -oblige, -organize, -pack, -pamper, -peacock, -pepper, -pet, -plum, -point, -polish, -possess, -preface, -promise, -prove, -provoke, -puff, -race, -rapturize, -regulate, -rehearse, -relax, -represent, -restore, -rev, -reward, -sauce, -scare, -scent, -season, -scrub, -secrete, -seed, -soak, -store, -sup, -sweat, -teach, -thick, -throng, -till, -vilify, -worry, -worship. 
 :::  A few such verbs occur in Old English, e.g. OVERDO v., OVERDRINK v., OVERFILL v., oferseman; some of these, however, only approach this sense, or can be otherwise explained. 
 :::(...) 

 :::    b. With other nouns expressing actions or conditions, whether identical in form with a corresponding verb, or combined with a suitable suffix (as -ion, -ment, -ure, -nce, -age, -ice, etc.). More established words of both types (as OVERBID n., OVERCHARGE n., OVEREXERCISE n., OVER-INFLUENCE n., etc.; OVERACHIEVEMENT n., OVERACTION n., etc.) are treated as main entries. So over-abuse, -arousal, -blame, -broil, -claim, -concern, -control, -demand, -drain, -ornament, -self-esteem, -worry; over-accentuation, -accumulation, -addiction, -aspiration, -assumption, -attachment, -attention, -civilization, -classification, -commitment, -consumption, -cultivation, -decoration, -devotion, -dilution, -distension, -drainage, -dramatization, -enrichment, -exaltation, -expansion, -expenditure, -flexion, -imitation, -importation, -insistence, -interpretation, -involvement, -lactation, -laudation, -legislation, -moralization, -multiplication, -nutrition, -organization, -ornamentation, -provision, -rapture, -recovery, -reflection, -regulation, -reliance, -repletion, -representation, -secretion, -service, -sophistication, -speculation, -tension. 
 :::   (...) 

 :::1849 Amer. Whig Rev. Mar. 290/2 The next year giving..to the one that was *over-represented a number less. 1881 Jrnl. Statist. Soc. 44 146 Both the dangers above referred to, viz., (1) of the majority in the constituencies being misrepresented in the assembly, and (2) of its being over-represented there. 1987 Amer. Sociol. Rev. 52 393 Our subsample overrepresents those with children. 

 :I think that at least the last definition matches my meaning. Can I go back now to my main argument?  
 :