Sounds like a interesting project. I think you´ll find some first hints here:

1: Schindler A, Hiller W, Witthöft M. What predicts outcome, response, and

drop-out in CBT of depressive adults? a naturalistic study. Behav Cogn

Psychother. 2013 May;41(3):365-70. doi: 10.1017/S1352465812001063. Epub 2012 Dec 5

2: Simon GE, Imel ZE, Ludman EJ, Steinfeld BJ. Is dropout after a first

psychotherapy visit always a bad outcome? Psychiatr Serv. 2012 Jul;63(7):705-7.

doi: 10.1176/appi.ps.201100309.

3: Carter O, Pannekoek L, Fursland A, Allen KL, Lampard AM, Byrne SM. Increased

wait-list time predicts dropout from outpatient enhanced cognitive behaviour

therapy (CBT-E) for eating disorders. Behav Res Ther. 2012 Aug;50(7-8):487-92.

doi: 10.1016/j.brat.2012.03.003. Epub 2012 Mar 30.

4: Martino F, Menchetti M, Pozzi E, Berardi D. Predictors of dropout among

personality disorders in a specialist outpatients psychosocial treatment: a

preliminary study. Psychiatry Clin Neurosci. 2012 Apr;66(3):180-6. doi:

10.1111/j.1440-1819.2012.02329.x.

5: Ravitz P, McBride C, Maunder R. Failures in interpersonal psychotherapy (IPT):

factors related to treatment resistances. J Clin Psychol. 2011

Nov;67(11):1129-39. doi: 10.1002/jclp.20850. Epub 2011 Oct 3. Review.

6: Simon GE, Ding V, Hubbard R, Fishman P, Ludman E, Morales L, Operskalski B, Savarino J. Early dropout from psychotherapy for depression with group- and

network-model therapists. Adm Policy Ment Health. 2012 Nov;39(6):440-7. doi:

10.1007/s10488-011-0364-x.

7: Dunn K, Delfabbro P, Harvey P. A preliminary, qualitative exploration of the

influences associated with drop-out from cognitive-behavioural therapy for

problem gambling: an Australian perspective. J Gambl Stud. 2012 Jun;28(2):253-72. doi: 10.1007/s10899-011-9257-x.

8: Kaplowitz MJ, Safran JD, Muran CJ. Impact of therapist emotional intelligence

on psychotherapy. J Nerv Ment Dis. 2011 Feb;199(2):74-84. doi: 10.1097/NMD.0b013e3182083efb.

9: Sharf J, Primavera LH, Diener MJ. Dropout and therapeutic alliance: a

meta-analysis of adult individual psychotherapy. Psychotherapy (Chic). 2010

Dec;47(4):637-45. doi: 10.1037/a0021175.

10: Masaki N, Toyomasu K. Factors for drop-out psychiatric treatment in patients

with substance-related disorders. Kurume Med J. 2010;57(3):67-72.

11: Levy KN, Meehan KB, Yeomans FE. Transference-focused psychotherapy reduces treatment drop-out and suicide attempters compared with community psychotherapist treatment in borderline personality disorder. Evid Based Ment Health. 2010 Nov;13(4):119. doi: 10.1136/ebmh.13.4.119.

12: Perroud N, Uher R, Dieben K, Nicastro R, Huguelet P. Predictors of response

and drop-out during intensive dialectical behavior therapy. J Pers Disord. 2010

Oct;24(5):634-50. doi: 10.1521/pedi.2010.24.5.634.

13: Villeneuve K, Potvin S, Lesage A, Nicole L. Meta-analysis of rates of

drop-out from psychosocial treatment among persons with schizophrenia spectrum

disorder. Schizophr Res. 2010 Aug;121(1-3):266-70. doi:

10.1016/j.schres.2010.04.003. Epub 2010 May 8.

14: Cuijpers P, Donker T, van Straten A, Li J, Andersson G. Is guided self-help

as effective as face-to-face psychotherapy for depression and anxiety disorders?

A systematic review and meta-analysis of comparative outcome studies. Psychol

Med. 2010 Dec;40(12):1943-57. doi: 10.1017/S0033291710000772. Epub 2010 Apr 21. Review.

15: McCabe MP, Price E. Attrition from an internet-based psychological

intervention for erectile dysfunction: who is likely to drop out? J Sex Marital

Ther. 2009;35(5):391-401. doi: 10.1080/00926230903065963.

16: Eskildsen A, Hougaard E, Rosenberg NK. Pre-treatment patient variables as

predictors of drop-out and treatment outcome in cognitive behavioural therapy for

social phobia: A systematic review. Nord J Psychiatry. 2010 Apr;64(2):94-105.

doi: 10.3109/08039480903426929. Review.

17: Cuijpers P, van Straten A, Schuurmans J, van Oppen P, Hollon SD, Andersson G.

Psychotherapy for chronic major depression and dysthymia: a meta-analysis. Clin

Psychol Rev. 2010 Feb;30(1):51-62. doi: 10.1016/j.cpr.2009.09.003.

18: Hamilton M, Wininger L, Roose SP. Dropout rate of training cases: who and

when. J Am Psychoanal Assoc. 2009 Jun;57(3):695-702. doi:

10.1177/0003065109337508.

19: Völlm B. Assessment and management of dangerous and severe personality

disorders. Curr Opin Psychiatry. 2009 Sep;22(5):501-6. doi:

10.1097/YCO.0b013e32832c9cdc. Review.

20: Campbell MA, Waller G, Pistrang N. The impact of narcissism on drop-out from cognitive-behavioral therapy for the eating disorders: a pilot study. J Nerv Ment Dis. 2009 Apr;197(4):278-81. doi: 10.1097/NMD.0b013e31819dc150.

21: Cuijpers P, van Straten A, Andersson G, van Oppen P. Psychotherapy for

depression in adults: a meta-analysis of comparative outcome studies. J Consult

Clin Psychol. 2008 Dec;76(6):909-22. doi: 10.1037/a0013075.

22: Chiesa M, Fonagy P, Bateman AW, Mace C. Psychiatric morbidity and treatment

pathway outcomes of patients presenting to specialist NHS psychodynamic

psychotherapy services: results from a multi-centre study. Psychol Psychother.

2009 Mar;82(Pt 1):83-98. doi: 10.1348/147608308X339512. Epub 2008 Aug 25.

23: Morlino M, Di Pietro G, Tuccillo R, Galietta A, Bolzan M, Senatore I, Marozzi

M, Valoroso L. Drop-out rate in eating disorders: could it be a function of

patient-therapist relationship? Eat Weight Disord. 2007 Sep;12(3):e64-7.

24: Bados A, Balaguer G, Saldaña C. The efficacy of cognitive-behavioral therapy

and the problem of drop-out. J Clin Psychol. 2007 Jun;63(6):585-92.

25: Mohr DC, Hart SL, Howard I, Julian L, Vella L, Catledge C, Feldman MD.

Barriers to psychotherapy among depressed and nondepressed primary care patients. Ann Behav Med. 2006 Dec;32(3):254-8.

Another hint, in my opinion (although focusing on adults), could be: Swift JK, Greenberg RP. Premature discontinuation in adult psychotherapy: a meta-analysis. J Consult Clin Psychol 2012; 80: 547-559.

Thank you very much for your help!

As I can see, the drop-outs were rather analyzed among adults...

Once again, thank you very much and best regards:)

Dear Magdalena - We're just starting to analyse some in-depth interviews with adolescents who've dropped out of psychotherapy (as part of an RCT study). We may well go back later and look at other predictors/determinants of drop-out, based on baseline data - so would be interesting to hear more about what you are working on, or if you've come across any interesting studies....