# Assuming the true mean

I've collected fluorescence data from some bacterial cells.

Each cell has a gene in it which can be induced to fluoresce. However, even without being induced, the gene will still fluoresce a little.

I have subjected the cells to a series of concentrations of inducer, including 0% inducer, and measured the resultant fluorescence over time.

The fluorescence produced from cells that have not been induced is, effectively, 'background' fluorescence. Therefore, I would like to subtract the background fluorescence from the fluorescence measured in cells that have been induced in order to determine the fluorescence that is caused by induction.

$n = 3$ for all measurements.

My question is, can I take the mean fluorescence of the uninduced cells and assume that it is the true mean? I.e. assume that its $SE = 0$. If I can do that, when I subsequently subtract the mean background fluorescence from the mean induced fluorescence, the final calculated $SE$ will be lower.

Here's some example data:

 Inducer:       0%              5%
1             3411            4965
2             3427            4784
3             3412            5379
Mean          3416.666667     5042.666667
SD            7.318166133     249.0385958


Given that the background will change for each experiment, I assume that the mean background measured is the true mean for that experiment. Is that not correct?

I must state that my maths/stats skills are rudimentary at best so please bear that in mind when answering.