Question

(7) The following values were obtained for the nitrate concentration (mg/L) in a sample of river water: 0.403, 0.410, 0.401, and 0.380. The last measurement is suspect. Based on this data set only, should it be rejected? Justify your answer.

(8) Three further measurements were added to those given in question (7) so that the complete results became: 0.403, 0.410, 0.401, 0.380, 0.400, 0.413, and 0.411. Should “0.380” still be retained/rejected? Justify your answer.

(9) Based on questions (7) and (8), formulate one paragraph with a procedure you will always follow upon facing “suspicious” results.

Answer 1

(7) The following values were obtained for the nitrate concentration (mg/L) in a sample of river water: 0.403, 0.410, 0.401, and 0.380. The last measurement is suspect. Based on this data set only, should it be rejected? Justify your answer.

The box plot is:

Since 0.380 is low, this value is an outlier and should be rejected.

(8) Three further measurements were added to those given in question (7) so that the complete results became: 0.403, 0.410, 0.401, 0.380, 0.400, 0.413, and 0.411. Should “0.380” still be retained/rejected? Justify your answer.

The box plot is:

Since 0.380 is too low, this value is an outlier and should be rejected.

(9) Based on questions (7) and (8), formulate one paragraph with a procedure you will always follow upon facing “suspicious” results.

We can use the box plots to check the precision of the suspected value. If the values are away from the box plot, then the value can be considered as a suspicious measurement which can help us in getting to the result to remove the value from the data set.