**Biostatistics and research methodology notes Unit 1**: Introduction Statistics, Biostatistics, Frequency distribution Measures of central tendency Mean, Median, Mode- Pharmaceutical examples Measures of dispersion Dispersion, Range, standard deviation, Pharmaceutical problems Correlation Definition, Karl Pearson’s coefficient of correlation, Multiple correlations – Pharmaceuticals examples

## Coefficient of Correlation

A coefficient of correlation is generally applied in statistics to calculate a relationship between two variables. The correlation shows a specific value of the degree of a linear relationship between the X and Y variables, say X and Y. There are various types of correlation coefficients. However, Pearson’s correlation (also known as Pearson’s R) is the correlation coefficient that is frequently used in linear regression.

## Pearson’s Coefficient Correlation

Karl Pearson’s coefficient of correlation is an extensively used mathematical method in which the numerical representation is applied to measure the level of relation between linearly related variables. The coefficient of correlation is expressed by **“r”.**

## Karl Pearson Correlation Coefficient Formula

## Alternative Formula (covariance formula)

## Pearson correlation example

1. When a correlation coefficient is (1), that means for every increase in one variable, there is a positive increase in the other fixed proportion. For example, shoe sizes change according to the length of the feet and are perfect (almost) correlations.

2. When a correlation coefficient is (-1), that means for every positive increase in one variable, there is a negative decrease in the other fixed proportion. For example, the decrease in the quantity of gas in a gas tank shows a perfect (almost) inverse correlation with speed.

3. When a correlation coefficient is (0) for every increase, that means there is no positive or negative increase, and the two variables are not related.

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