Statistics ? Descriptive statistics Vs Inferential statistics

Why Statistics Matters More Than Most People Realize

Statistics come from word “Statista” which is an Italian word which means any statement It came in to picture somewhere in 1660. It was first discovered by Gottfried Achenwall, who was a German philosopher, economist and one who invented the statistics. He is also known as “Father of Statistics”.

Later on Sir John Sinclair popularized this concept to even further heights. Statistician is person who use statistical tool and techniques to interpret data. Sir Ronald Aylmer Fisher contribution to this field of statistics was immense hence he is known ad “The Father of Modern Statistics”. He worked on Design of Experiments.

Statistics play very important role in some critical decision-making situations. Statistics help us make sense of the vast amount of information in the world as through see though your eyes and listed through your ears, you can filter out vast number of unnecessary stimuli which may not be useful to us.

What Statistics means to you may be different for someone else. Take an example scientist use statistics on daily basis to predict the weather  forecast for each and every day. Statistics is all about making sense of data collected and analyzing, interpreting, and then figuring out how to put that information to best of use. Today, in this blog, we’re going to answer all these questions.

Why Beginners often Confuse Descriptive Statistics and Inferential Statistics

Descriptive Statistics: Understanding the Data You Already Have

Inferential statistics is the branch of statistics that uses data from a sample to draw conclusions about a larger population. This is the point where statistics becomes especially powerful, because in real life we often cannot study every single member of a population. Inferential statistics makes good inferences and near perfect predictions about a population based on a sample of data taken from the population. Inferential statistics help us make decisions about data’s uncertainty.

Let’s understand the difference between these two with help of an example:

Suppose you are evaluating average marks scored by Class 7A in Science subject. Since you are evaluating the performance of Class 7A only using the data that you have collected either through numerical calculations or graphs or tables and are not making any generalized conclusion about other batches of class 7. This is called Descriptive statistics.

Now you decide that based on this data of Class 7A, I want to estimate the average marks in all other sections of Science. Now this way of estimating we call it Inferential Statistics. So, any conclusion or inference that we can draw from this data tell us how that data would be. Statistician call it Statistical Inference.

Categories of Descriptive Statistics :

Descriptive statistics often categorized as

  1. Measure of Central Tendency
  2. Measure of Spread
  3. Measure of Shape

Categories of Inferential Statistics :

Measure of Central Tendency

When people begin learning descriptive statistics, one of the first ideas they encounter is central tendency. In Descriptive statistics, central tendency (or measure of central tendency) which is a single point middle value describing data set by identifying its Mean, Median and Mode. Measure of central tendency gives the location. Measure of Central tendency is also known by another name “Measure of Location“. Click this YouTube video link for detailed understanding.

Mean

Average of all values. Most popular measure of descriptive statistics. The mean is useful because it includes every value in the dataset. But it can be affected strongly by unusually high or low values. Say for examples we have n values of data having individual values as A1, A2, A3….An . Then mean or arithmetic mean is calculated as A1+ A2+ A3+….An/ n.

Assume the following data set :  10,20,30,20,40,20,10

Sum = 10+20+30+20+40+20+10 = 150 ; N= 7

Mean = 150/7 = 21.42

The mean of these data is 21.42

Median

The median is the middle value when the data is arranged in ascending or descending order. If there is an odd number of values, the median is the middle one. If there is an even number of values, the median is the average of the two middle values. The median is especially useful when data is skewed or contains extreme values. First thing , we need to arrange the data in ascending order.

– If number of value is ODD, then the median is the middle value when arranged in ascending order.

– Is number of value is EVEN, the median is the average of two middle value when arranged in ascending order.

Assume the following data set :  10,20,30,25,40,35,10

Arranging in ascending order : 10, 10, 20, 25, 30, 35, 40

Median is 25 (Since number of value is “Odd”)

Lets take another example when data set is “Even”

Assume the following data set :  10,20,30,25,40,35,10, 20

Arranging in ascending order : 10, 10, 20, 20, 25, 30, 35, 40

Median is 20+25/2= 22.5 (Since number of value is “Even”)

Mode

The mode is the most frequently occurring value. In some datasets there is one mode, in others there may be more than one, and sometimes there is no repeated value at all. The mode is especially useful for categorical data, such as favorite subject, preferred mobile brand, or most common blood group. Most frequent occurring value in a set of data values

Assume the following data set : 10, 20, 30, 20, 40, 20,10

Most frequent occurring value =20

Measures of Dispersion: How Spread Out Is the Data? Measure of Spread

Knowing the center of the data is helpful, but it is not enough. Two datasets can have the same average and still be very different. That is why descriptive statistics also uses measures of dispersion, sometimes called measures of spread or variability. Measure of Spread is also known by another name “Measure of Dispersion“. It defines how the data is spread or scattered.

Assume the following data set :  49, 50, 58, 58, 60, 62, 66, 68, 70, 72

Average = 61.3

Range: R = max – min. = >          = 72- 49 = 23

Variance and standard deviation provide a deeper view. Variance measures how far values tend to lie from the mean. Standard deviation is the square root of variance and is often easier to interpret because it is in the same unit as the data.

Variance: The standard deviation is simply the positive square root of the variance

Standard Deviations: The standard deviation is simply the positive square root of the variance. A lower standard deviation means values are clustered close to the average. A higher standard deviation means values are more spread out

Measure of Shape

Measures of shape describe how the data is distributed. Measure of Shape is further categorized in to two types : Symmetry and Modality

Skewness

Skewness measures spread of data, whether its symmetrical or skewed to Left or Right. If it is skewed to the right it is called Positive Skewed and if it the left it is called Negative Skewed. Skewness measures typically range from -3 to +3. Skewness vale of “0” is considered “Normal” .

Symmetric : Mean=Median=Mode ( Normal Distribution )

Left skewed : Mean<Median

Right skewed : Median< Mean

Kurtosis :

Kurtosis measures peak of data. whether its heavy tail or light tail. Kurtosis measures typically range from -3 to +3. Kurtosis value of 3 denotes normal distribution. Normally 3 types of kurtosis are there : Mesokurtic, Leptokurtic and Platykurtic.

Mesokurtic:kurtosis value = 3 ( Normal Distribution )

Leptokurtic: kurtosis value > 3

Platykurtic: kurtosis value < 3

Modality

Unimodal : Distribution with single peak

Bimodal Distribution with two peak

Multimodal : Distribution with more than two peak

FAQ on Descriptive statistics Vs Inferential statistics

I hope this blog helped in understanding the basic concept in a simplified manner, watch out for I hope this blog helped in understanding the basic concept in a simplified manner, watch out for more such stuff in the future.



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