Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
DESCRIPTIVE STATISTICS The simplest form of single-variable analysis is to count the number of cases in each category; the resulting count is called a frequency distribution. A frequency distribution is often not very interesting without additional statistical manipulations. The nature of these manipulations depends on the type of variable or, more accurately, on the level of measurement. CENTRAL TENDENCY OF DATA Measures of central tendency are used to describe the location or "centre" of the data. The mean, the mode, and the median are measures of central tendency. To decide whether the mean, the mode or the median best represents the central tendency for a certain distribution, one must consider the strengths and weaknesses of each measure. The mean (“µ” in the population in the sample) is obtained by adding the scores and dividing the total by the number of scores. The mode measures the greatest frequency. In a frequency distribution, the mode represents the highest point. The median Is the middle value when the scores are arranged in order of increasing magnitude Advantages Disadvantages Because of the statistical properties of the mean, such as efficiency and consistency, and because the deviation of the mean is always equal to zero, the mean is generally considered to be the best estimation of the central tendency. It is simple to calculate and comprehend The mean is affected by extreme values. The occurrence of a few extreme values can completely distort the appearance of the distribution The mean could hide peculiar distortions of data distribution (e.g. it would not show if the data set is bimodal) There can be more than one mode value (e.g. bimodal data set) or none (i.e. no data is repeated) The mode is very sensitive to changes in size and in the number of class intervals in the frequency distribution, i.e. the modes could change just by changing the way one builds the frequency distribution It is less sensitive to group data in intervals Being a stronger measure, it is useful when the distribution of the characteristics are asymmetrical 1 3 4 7 10 13 18 23 125 UNICEF M&E Training Resource Module 6.1.1 Descriptive statistics - Page 1/2 VARIANCE IN THE DATA Often, the evaluator may want to know how individuals within a group differ from the average or central tendency of the group. The range Advantages Disadvantages It is very easy to calculate It depends only on the highest and lowest score: can be misleading It is a very powerful measurement to describe the variation of scores Knowing the standard deviation allow us to differentiate between values that are usual and those that are unusual Is the difference between the highest value and the lowest value. For example, if the average age of a group of mothers using ORT were 28, a key question would be “What is the range in ages of the group?” In other words, what is the age of the youngest mother using ORT and the oldest? The standard deviation gives the average distance of individual measurement observations from the group mean. If the scores are distributed according to a normal distribution (i.e. the bell shaped curve – a Gaussian – shown in the picture), then: 99,7 % of data are within 3 std deviation of the mean 95% within 2 std deviation 68% within 1 std deviation mean Standard deviation UNICEF M&E Training Resource Module 6.1.1 Descriptive statistics - Page 2/2