The number of malaria cases repoed during the last 10 years in a town is given below, 250, 320, 190, 300, 5000, 100, 260, 350, 320, and 160. The epidemiologist wants to find out the average number of malaria cases repoed in that town during the last 10 years. The most appropriate measure of average for this data will be-

Ans. is 'c' i.e., Median o As already explained measures of central tendency (statistical average) are ? i) Mean (arithmetic mean) ii) Median iii) Mode o In the given set of values of incidence of malaria one value (i.e. 5000) is an extreme score . o This extreme score will highly effect the mean. Mean is very sensitive to extreme scores. Mean in this case would be =960 which does not at all represent the average incidence of malaria in the area. o Median is insensitive to extreme scores in a distribution. The median would not be effected by the extreme value of 5000.Median in this case is 300 which is nearer to the truth and therefore is a better representative of the incidence of malaria in past 7 yrs. o Mode is also not effected by the extreme values in the observation but it is difficult to calculate therefore not used to express the averages. o In distribution with extreme values - i) Most affected measure of central tendency mean ii) Least affected measure of central tendency --> mode iii) Most preferable measure of central tendency --> median