input: The following are multiple choice questions (with answers) about medical knowledge.   **Question:** Please refer to the summary above to answer this question The authors of the study have decided to conduct a follow-up analysis on their data. They decide to stratify their results by CD4+T-lymphocyte count at the time of diagnosis. Among patients with CD4+ cell counts below 200/mm3, cART adherence was a significant predictor of DLBCL risk (RR = 0.52, p = 0.01). However, among patients with CD4+ cell counts above 200/mm3, no relationship was found between DLBCL risk and cART adherence (RR = 0.96, p = 0.36). Which of the following explains for the difference observed between the two strata?"   (A) Poor generalizability   (B) Stratified sampling   (C) Random error   (D) Effect modification
output: ['(D) Effect modification <> answer', 'The following are multiple choice questions (with answers) about medical knowledge. <> instruction', '(A) Poor generalizability  (B) Stratified sampling  (C) Random error  (D) Effect modification <> possible answers', '  Please refer to the summary above to answer this question\nThe authors of the study have decided to conduct a follow-up analysis on their data. They decide to stratify their results by CD4+T-lymphocyte count at the time of diagnosis. Among patients with CD4+ cell counts below 200/mm3, cART adherence was a significant predictor of DLBCL risk (RR = 0.52, p = 0.01). However, among patients with CD4+ cell counts above 200/mm3, no relationship was found between DLBCL risk and cART adherence (RR = 0.96, p = 0.36). Which of the following explains for the difference observed between the two strata?" <> context']