Intentional differences
In experiments, different 'individuals' are given different experimental treatments with the intention of comparing these treatments. We hope to find whether changing the experimental treatment causes differences in the measurements.
Signal and noise in experimental data In experimental data sets, the variability caused by different experimental conditions is the signal in the data since the intention of the experiment is to determine the effect of these differences. However the signal in the data is usually obscured by the natural variability in the data — the noise in the data set. In the experimental data on the right, it is difficult to assess whether the fertiliser has increased plant yield because of the natural variability between plants. |
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Statistics tries to estimate the signal from data that also contain noise.