Inclusion Criteria:  Group 1 (IBS-C)  ≥18 years old Decrease of frequency of bowel movement (<3 time per week), change of stool consistency (stool that is hard and difficult to pass, Bristol Types 1 to 3), or other 'constipation symptoms' judged by investigators. With abdominal symptoms such as abdominal pain, bloating, and abdominal discomfort, or other 'constipation symptoms' judged by investigators. Result of ROME VI marked as 'IBS-C'.  Group 2 (non-IBS-C)  ≥18 years old Decrease of frequency of bowel movement (<3 time per week), change of stool consistency (stool that is hard and difficult to pass, Bristol Types 1 to 3), or other 'constipation symptoms' judged by investigators. With abdominal symptoms such as abdominal pain, bloating, and abdominal discomfort, or other 'constipation symptoms' judged by investigators. Result of ROME VI marked as 'Non IBS-C'.  Exclusion Criteria:  Individuals with a cognitive condition and unable to finish the questionnaire. Individuals have an acute or chronic non-GI condition that can be associated with constipation; e.g., central nervous system cause (Parkinson's disease, spinal cord injury, and multiple sclerosis), pseudo-obstruction, colonic inertia, megacolon, megarectum, bowel obstruction, descending perineum syndrome, solitary rectal ulcer syndrome, systemic sclerosis.  Individuals who had been diagnosed with the following organic health problems likely to affect GI symptoms:  Inflammatory bowel disease (Crohn's disease or ulcerative colitis) cancer anywhere in the GI tract or current infection of the GI tract. Pelvic floor dysfunction. (i.e., disease that is not adequately treated or stable with therapy.) Any history of colon surgeries. Individuals who participate in any interventional study currently. Not suitable for the study judged by investigators.