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How to use Standard Deviation and Co-efficient of Variation.

Updated on February 20, 2013
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A qualified Textile Post Diploma Graduate and Ex.M D of a Textile Mill.

Graph - Courtesy - WIKIPEDIA.
Graph - Courtesy - WIKIPEDIA.

Check the Health of your School Kids by SD and CV of Statistics not by a MD in Medicine.

Class by Class and at each Grade in your school you record the weight and height of each student.Let's take Class A Grade 3.The weight and height gives the Body Mass Index of each student.If there are 30 students and you have 30 numbers representing the BMI* of each student.Take a graph sheet and draw a line vertically call it 'Y' axis.draw another line horizontally and call it as 'X' axis.The line 'X' and 'Y' will be in the shape of letter ' L '.

At the point where 'X and 'Y' meet it is zero count 5 lines vertically and call it 1 the next 5 divisions 2 and so on till you have 30 such sections on the graph ( the graph sheet must have ten lines in one inch.The graph sheet must be wider than 20 inches and the height must be length wise the same 25 inches or more as BMI will not go higher than 35.

From 1 to 30 mark the BMI of each student and join these points from 1 to 30.The picture of the line will be or must be of the shape of a bell as shown in the picture above.Draw the lines as shown in the pictures if it gives the same or very near to the percentages on either side your students are all in normal health but it is showing that students of higher BMI contribute to your graph what do you do.Meet the students parents and show them the boys number say 13 or 15 and tell them that these students need to maintain normal standard BMI that a grade 3 student must have.The graph in this case if all the boys fall in standard BMI than you will not get a bell shape but a line which is very rare.

Further calculations will be to add all the 30 numbers and this number will be ' x '.( sum of all numbers ).

Divide this number 'x' by 30 ( the number of students.)which we call as -> x (bar) by placing a line over x.

Next subtract BMI number by x (bar) for each student which you call as n1 to n 30.

Next n1 to n30 square each of the number.

Total all the numbers from n1 to n30 call it 'Y1'.

Next subtract from 30 the number 1 which will be 29.

Next divide 'Y1' by 29 this will be the SD.

It is OK to know SD which may be (-) or (+).How significant it is is known by CV% which has got to be below 1.

So now you have to know the square root of SD which you call it as 'S'

Divide 'S' by ' x ' this you call as CV % which must be below 1 and never above 1,if its above 1 the student needs a doctor now which would other wise be a heavy medical check expenditure to take care of the normal health of all students periodically.

You can ask the students to give the BMI to the leader of the class who shall personally supervise the exercise.

* BMI is Body Mass Index.


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