BMC Public Health 2009, 9:214 http://www.biomedcentral.com/1471-2458/9/214 Sampling and sample size calculation All asylum seekers and refugees included in this study were 18 years of age or above. As a family tend to have similar values for some of the outcomes studied, only one member per family was randomly selected on the basis of a registration code. Offshore refugees were excluded from the study as they are granted refugee status prior to arrival in Ireland and have never been through the asylum process. The sample size was calculated based on the results of a previous study that reported the proportion of asylum seekers and refugees with PTSD symptoms using the Har- vard Trauma Questionnaire (HTQ) scoring system [7]. We planned to recruit between 53–66 asylum seekers and 27– 33 refugees, assuming a difference in the proportion of patients with PTSD symptoms to be 32.4% (43.4% for asylum seekers and 11% for refugees) [7]. This would give the study a power of between 80–90% at a significance level of 0.05. The recruitment was carried out over a three month period (February to April 2007). A random sample of asylum seekers (66 people) were selected from the register of the two direct provision centres and asked to participate in the study. For the refugee sample, Community Welfare Offic- ers have a register of the refugees living in their catchment area, and a random sample from this register (33 people) were asked to participate in the study. A) Health Status Outcome Measures We assessed three principal outcomes in relation to health: general health status; symptoms of PTSD; and symptoms of anxiety and depression. For analyses, the health outcome variables were dichotomised as follows. 1. General health status – current health status of respondents was measured according to the general health questions on the 36-item Short-Form (SF-36) [8]. The response options ranged from '5 = excellent' to '1 = poor' and were subsequently dichotomised into: 'good' (excellent, very good, good) and 'poor' (fair, poor). Although not originally developed for use in migrant pop- ulations, the SF-36 has been translated into numerous languages for use in research. However, it should be noted that its cross cultural validity has been questioned [5]. 2. PTSD status – part IV of the Harvard Trauma Question- naire (HTQ) was used [9]. It includes 30 symptoms, of which 16 were derived from the Diagnostic and Statistical Manual of Mental Disorders (DSM-III-R) criteria for PTSD and 14 describe symptoms related to the traumatic events in the refugees' lives. The format of the response options is comparable to that of the HSCL-25 (item 3 below). Individuals with a mean score on the 16 PTSD symptoms and/or on the total list of 30 symptoms = 2.5 were consid- ered to be symptomatic for PTSD. This scale was devel- oped for use in refugee populations and has been used in numerous studies on refugees [1,5]. The 2.5 cut-point was chosen to make our study comparable to others, however, it should be noted that the validity of this cut point has only been demonstrated in outpatient psychiatric patients and not in a community based setting [5]. 3. Anxiety and depression status – the Hopkins Symp- tom Check List-25 (HSCL-25) [10,11], was used to meas- ure symptoms of anxiety (10 items) and depression (15 items). Respondents were asked to indicate the extent to which they were bothered by each symptom in the previ- ous week, ranging from '1 = not at all' to '4 = extremely'. Individuals with a mean score for anxiety and/or depres- sion and/or the total list of symptoms > 1.75 were consid- ered to be symptomatic. This instrument wasn't originally designed for use in refugee populations but has been adapted [11], and subsequently used in a number of refu- gee studies [1,5]. The cut point of 1.75 was chosen so our results would be comparable with other studies. However, the validity of this cut point in community based refugees and asylum seekers of multiple nationalities is unclear. Explanatory variables To explore the influence of potential explanatory variables on general health, PTSD and depression/anxiety, we assessed the following: 1. Residence status – refugee or asylum seeker. 2. Pre migration stressors – Pre migration stressors (trau- mas) were assessed with part 1 of the HTQ, which includes 17 events (e.g. lack of food and water, being close to death) with three possible responses (experienced, wit- nessed, no) [9]. An additional 15 traumatic events (e.g. rocket attacks) were added to the questionnaire by Gerrit- sen and colleagues based on Amnesty International Annual Reports (1975–2002) [6] as well as items from HTQ part III that focus on traumatic events. This variable was dichotomised into '0 to 7 pre migration traumas' and '≥ 8 pre migration traumas'. 3. Post migration stressors – Respondents were asked about possible stressful experiences they have experienced in Ireland. The checklist included 18 problems often reported by refugees in research on post migration stres- sors (e.g. uncertainty about residence status, loneliness, discrimination and communication problems) [6,12-14]. They were asked to indicate the extent to which any of the items had bothered them in the previous month ('1 = not at all' to '4 = extremely'). A mean score was calculated and dichotomised into < 2.5 and ≥ 2.5 events [15]. Page 3 of 10 (page number not for citation purposes)