We followed the STROBE (Strengthening the Reporting of Observational studies in Epidemiology) directive guidelines for observational studies . The Approval of the study protocol was obtained from the institutional ethics review board (number : 79/17 ) and all patients enrolled in the study provided a written, informed consent allowing the use of their data for clinical studies at the time of their initial visit.
Description of the instruments
The participants completed in addition to a general information section including sociodemographic and clinical data, the EORTC QLQ-CR29 , and the validated Moroccan Arabic version of the QLQ-C30 (version 3.0). 
The EORTC QLQ-C30 includes five functional subscales (i.e., physical functioning, role functioning, emotional functioning, cognitive functioning, and social functioning), three symptom subscales (i.e., fatigue, nausea and vomiting, and pain), a global QoL subscale, and six single symptom items (i.e., dyspnea, insomnia, appetite loss, constipation, diarrhea, and financial difficulties). The scoring of items is on a 1 to 7 and 1 to 4 Likert scales for the global health status/quality of life and the other scales. High scores represent better functioning and worse symptoms. 
The EORTC QLQ-CR29:
The EORTC QLQ-CR29 is a colon and rectum site-specific quality of life module with 29 items consisting of 4 multi-item scales (body image, urinary frequency, blood and mucus in stool, and stool frequency) and 17 functional/symptomatic single-items (sexual interest, urinary incontinence, dysuria, abdominal pain, buttock pain, bloating, dry mouth, hair loss, taste, flatulence, fecal incontinence, sore skin, embarrassment, stoma care problem, impotence or dyspareunia). Among these items, only body image, anxiety, weight, and sexual interest are functional scales.
The eighteenth item (Q18) is an indicator of colostomy/ileostomy construction and following, items are separately arranged for patients with a stoma (Q19-Q25) and without (Q19-Q25) according to symptoms of stool frequency, flatulence, fecal incontinence, sore skin and embarrassment while item 25 is specific for stoma care. Sexual interest, impotence and dyspareunia items are categorized according to gender with the corresponding questions being Q26-Q27 and Q28-Q29 for male and female respondents respectively. All questionnaire items ask about the past week except the ones on sexuality, which request the patients to evaluate the past four weeks. As regards the scoring, the multi-item scales and single items are scored using a 1 to 4 point Likert scale (“not at all”, “a little”, “quite a bit”, “very much”) with the highest score representing the best functional status or the worst symptom .
Translation process :
The translation process followed the European Organisation for Research and Treatment of Cancer (EORTC) guidelines . Two different translators independently translated the questionnaire from English to Moroccan Arabic and a consensual version was attained following the discussion of both translations. Back translation into English was then performed by two different translators who had no prior knowledge of the original English version. An expert committee including surgeons, oncologists, epidemiologists and the four translators reviewed all translations and a provisional version was developed. To examine patients' understanding of the translated version, the provisional Moroccan Arabic EORTC QLQ-CR29 underwent a preliminary test on a group of 34 patients with colon or rectal malignancies after which the final version of the instrument was generated.
Study population and data collection :
Patients were prospectively recruited from the national oncology institute during the period between November 2019 and January 2020. Patients aged over 18 years with a pathologically confirmed cancer of the colon and/or the rectum who had undergone surgery at least 6 months prior to the enrollment in the study were included. Patients were excluded if they were unable to understand the questionnaire, presented cognitive and/or medical complications that hindered the interview completion and the submission of an uncompleted questionnaire. Participants were either approached during follow up visits or contacted via telephone. Patient’s characteristics were reported according to age, gender, stoma status, cancer localisation (colon vs rectum), neoadjuvant radiochemotherapy and adjuvant chemotherapy.
As the sample size determination for psychometric validation studies lacks clear recommendations , we determined the required sample by allocating a number of observations 5 to 10 times greater than the variables. Accordingly, the sample needed size ranged between 150 and 300 participants.
The scores for the QLQ-CR29 and the QLQ-C30 questionnaires were linearly converted into 0 to 100 point scores according to the standard EORTC guidelines. 
Descriptive statistics were generated through mean, median, standard deviation (SD), and floor and ceiling effects and age was categorized in 3 groups: < 40 years ; 41- 65 years and > 65 years.
There are two different levels of reliability; internal consistency and reproducibility.
Internal consistency reliability was determined using Cronbach’s alpha coefficient with a score greater than 0,7 considered acceptable, above 0,8 was good and higher than 0,9 was considered excellent.
As for reproducibility, a random subgroup of patients was selected to retake the QLQ CR-29 questionnaire after 7 to 14 days from the first interview to examine the test-retest reliability. The results of the two measurements were assessed using the Intraclass correlation coefficient (ICC) and an ICC score of 0,7 or higher was considered acceptable.
We tested the construct validity of the EORTC QLQ-CR29 using multitrait scaling analysis.  Convergent validity was examined by correlating each item with its own scale with an item-scale correlation of ≥0.40 equivalent to high correlation. Divergent validity on the other hand was tested by demonstrating that the item correlated higher with its own scale than with the others.
Concurrent validity was examined by comparing the scores of the QLQ-CR29 and the QLQ-C30 using Pearson’s correlation.
Clinical validity was assessed using known group comparison through the Mann Whitney U test to examine the QLQ-CR29’ ability to differentiate clinically distinct patients. Subgroups were categorized according to : age (<65 years vs ≥65 years ), gender (male vs female), stoma status (permanent vs no stoma), tumor site (colon vs rectal ) and neoadjuvant radiotherapy (no vs yes). All statistical analyses were performed using SPSS 26.0 (SPSS Inc., Chicago,IL, USA). Statistically significant results were defined with a P < 0.05 .