Mean The mean is the average of two or more values. It may be simple are weighted mean.

Simple mean The simple mean (X) of a given set of values is the sum of all the values (x) divided by the number of these values (n).

Weighted Mean Weighted mean is used when some values are more importance than others, the weighted mean is used. Each value (x) is assigned a weight (w) and multiplied with corresponding weight. The resulting products are added and divided by the total of the weights. The weighted mean is mostly used for the purpose of standardization.

Standardization Often when comparing indicator values we use data related to different groups within a population. Since these groups are likely to differ with respect to various characteristics, when analyzing one characteristics, it is important to remove the effect of the others, helping use to identify real differences and to begin to from ideas about their causes. This is done by standardization.

Ratio A ratio is the relationship between two quantities measured in the same unit. It is expressed as one value divided by another. The result possesses no unit.

Proportions When a ratio takes the form of a part divided by the whole it is called a proportion. A proportion is a special type of ratio in which the denominator is quantity that represents the whole of given group under investigation, and the numerator is a subset of it.

Rate When a relationship between tow quantities is measured by a quotient, and the numerator and denominator are expressed in different units, then the quotient is called a rate. The rate is usually expressed in terms of numerator-units per denominator-units.

Quintiles Quantiles are points taken at regular intervals from a set of ordered data that divide the distribution into ‘n’ equal –sized subsets. In this way quantiles are the data values that mark the boundaries between those subsets. For example ‘n’ can take the value of 10, which is to say that the set of values is divided into ten subsets. In this case, quantiles are called deciles.

Range The range is the difference between the highest, max (x), and the ‘lowest’ element, min (x), of a dataset.

Standard Deviation The standard deviation is a measure of dispersion around the mean of a data set. It is calculated by taking the positive square root of the variance.

Confidence Intervals A confidence interval (CI) is a quantitative expression of the uncertainty in a measurement. They are usually reported as a 95% CI, which is the range of values with in which we would expect that in 95 times out of 100 the true value for the whole population would lie. For example, if from a single sample we compute a mean height of 159 cm and a 95% CI of +/-8, we are saying that 95 times out of 100 the true value of the mean height for the whole population would fall between 151cm (159-8) and 167cm (159+8).