Commit fd134814 authored by Vallo Varik's avatar Vallo Varik
Browse files

Add task 10

parent 0591116c
......@@ -134,3 +134,16 @@ Good, filtering for `Time_h` between 9.5 and 10.5 h gives a desired result.
azithromycin excerts 95% effect. Can you calculate that with confidence
intervals?
10. There is one more thing. An intricacy. We have fitted and plotted (i.e.
think about it) the `x`, the concentration, in logarithmic scale, but the
IC~50~ is in linear scale. Mostly, it does not matter much. You can see
above, however, that the lower confidence interval is 5x lower than IC~95~
and the upper limit is less than 2x higher. One side is 5 away, the other
less than 2x. To fix that, one could estimate IC~50~ in log scale
(substitute IC~50~ in the 4-parameter logistic regression with
log(IC~50~)). One might have to take some time to think about it what that means. Luckily, `drm` makes all this easy. You fit the model exactly as
you did before, but this time, set `fct` to `LL2.4()`. Finally, when
calculating MIC, the confidence interval should be set to "fls" (`interval
= "fls"`).
Now the MIC (IC~95~) should be the same (33 µM), but the confidence interval are symmetric, about 2x lower and 2x higher.
......@@ -141,3 +141,19 @@ result.
azithromycin excerts 95% effect. Can you calculate that with
confidence intervals?
4. There is one more thing. An intricacy. We have fitted and plotted
(i.e. think about it) the `x`, the concentration, in logarithmic
scale, but the IC<sub>50</sub> is in linear scale. Mostly, it does
not matter much. You can see above, however, that the lower
confidence interval is 5x lower than IC<sub>95</sub> and the upper
limit is less than 2x higher. One side is 5 away, the other less
than 2x. To fix that, one could estimate IC<sub>50</sub> in log
scale (substitute IC<sub>50</sub> in the 4-parameter logistic
regression with log(IC<sub>50</sub>)). One might have to take some
time to think about it what that means. Luckily, `drm` makes all
this easy. You fit the model exactly as you did before, but this
time, set `fct` to `LL2.4()`. Finally, when calculating MIC, the
confidence interval should be set to “fls” (`interval = "fls"`).
Now the MIC (IC<sub>95</sub>) should be the same (33 µM), but the
confidence interval are symmetric, about 2x lower and 2x higher.
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