Simulations of spatial biases. The upper panels represent microarray images with introduced biases in yellow (arbitrary scale colorcode). The biases in panels 1–4 are subarray biases, in 5–10 horizontally-shaped biases and in 11–14 vertically-shaped biases. The lower panel shows the resulting autocorrelation pattern of each particular bias. Individual subarray effects cannot explain the observed autocorrelation periodicities, while large spatial biases give rise to various periodicities, depending on their shape.