How to find doubling time of cells with scatterplot in R?

Question

I\'m trying to calculate the doubling time of cells using a scatterplot. This is my dataframe

df = data.frame(\"x\" = 1:5, \"y\" = c(246, 667, 1715, 4867, 11694)         


        

Answer 1

You can plot the points to show the exponential rise and then linearize the function by applying log2 to the y values. With that you can plot and do a linear fit:

 df = data.frame("x" = 1:5, "y" = c(246, 667, 1715, 4867, 11694))
 plot(df)  # plot not displayed
 plot(df$x, log2(df$y))
 abline(lm(log2(y)~x,df))

 lm(log2(y)~x,df)
#-------------------
Call:
lm(formula = log2(y) ~ x, data = df)

Coefficients:
(Intercept)            x  
      6.563        1.401    #the x-coefficient is the slope of the line
#---------------------

log(2)/1.4

#[1] 0.4951051

Checking with the original (not-displayed plot that does look like a sensible estimate of doubling time. Be sure to cite this posting if this happens to be a homework problem.

If I were tasked with using the original graph, first draw an exponential curve by hand. I would then draw two horizontal lines at y= 2000 and y=4000 and then drop perpendicular lines from their intersections with the curve and read off the difference in x values on the horizontal axis.That is what I meant by my comment above that I "checked" the log2/x-coef value for sensibility.