The simulated data set contains expression levels of 2 gene probes for 50 cases and 50 controls. The expression levels of probe1 are generated from \(N(0, 1)\). The expression levels of probe2 for controls are also generated from \(N(0, 1)\). The expression levels of probe 2 for cases are generated from the formula \(probe2_{i} = -probe1_{i} + e_i\), \(i=1, \ldots, nCases\), where \(e_i\sim N(0, 0.3^2)\).
That is, the expression levels of probe 1 and probe 2 are negatively correlated in cases, but not correlated in controls.