Estimation of CDF on entire data set Encouraged by the results described in the previous section, we estimated the CDF that minimizes the sum of squared residuals over the entire data set. The results are depicted in Figure 7 . Fitting CDF on entire data set by minimizing the sum of squared residuals. These results raise the immediate question as to why the time costs are so low. A time cost of 1 cent a minute is only 60 cents an hour.
Several hypotheses suggest themselves.
Users are non-representative. This is likely part of the story. Our users are volunteers, many are students, and it is apparent from Figure 4 that certain occupations have much higher time values. The only way to deal with this is to try to repeat the study with a different sample, which we hope to do. Other uses of time.