Although the risk of IHD development was greater in the low-income group than in the high-income group [RR (95% CI) for period 2: low-income group, 1.77 (1.52, 2.07); high-income group: 1.47 (1.31, 1.65)], the difference was marginally significant (p-value for heterogeneity: 0.06) (Table S5 , see Additional file 1).
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