# Course — Statistics Foundations: The Basics

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**Objective of writing: **Preparing Notes or my learnings from course — Statistics Foundations: The Basics. Don’t have any intention to spam.

*Mean, Median and Mode*

Mean → Average

Mean of all 3 above dataset is same but points very far apart from each other in all 3. Hence, variability (range and standard deviation) in data is very important to measure.

Median → Middle element of data

Mode → Frequency of data (Most common value in dataset). Dataset may have no mode, single mode or multiple mode value

**Message** →Two students performing significantly poor, lowers down the average. If these two student have to complaint on exam, professor may ask to refer median.

*Z-Score*

If we have to tell, how far is `231` from Mean, one way of telling is 231 is 92 far from mean. We can use Z-Score to tell how far is data point from mean and in standard deviation

It means that data point `231` is 2.24 standard deviation from the mean in positive direction.

If z-score is -ve, it tells that point is less than mean.

*Standard Deviation*

Avg. square distance from mean

One dataset having Standard deviation of 20 and other dataset having standard deviation of 200. Which data have less variation ?

Ans. is it really depends, Like if 20 degree Celsius standard deviation in temperature in Paris in summer, its really high no.

Std. deviation can be used to study each data point as well. Consider below example, having 2 person’s salary ..

Person1 is Mean + 2 std. dev

Person2 is Mean -1 std. dev

*Empirical Rule*

Assuming, data is normally distributed, Most of data points in a given data set fall within 3 std. deviation of the mean.

*Outlier*

Data point that is an abnormal distance from the other values in the data set.

That’s all we have in this course. Thank you for reading.

Please clap if it helped you !!

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