Correlation
Quantitative A Aptitude & & Business S Statistics
Correlation Quantitative A Aptitude & & Business S - - PowerPoint PPT Presentation
Correlation Quantitative A Aptitude & & Business S Statistics Correlation Correlation is the relationship that exists betw een tw o or more variables. If tw o variables are related to each other in such a w ay that change
Quantitative A Aptitude & & Business S Statistics
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exists betw een tw o or more variables.
each other in such a w ay that change increases a corresponding change in other, then variables are said to be correlated.
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and weights.
demand of commodity.
insulin and blood sugar.
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studies relationship between variables like price and quantity demand.
deriving precisely the degree and the direction of such relationships.
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reduce the range of uncertainty
correlation analysis will more reliable and near to reality.
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the same direction ,correlation is said to be positive .
variable decreases ,the other also decreases ,then the tw o variables are said to be positive.
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said to be Negative.
decrease or ,if one variable decreases ,the other also increases ,then the tw o variables are said to be Negative .
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Methods of studying correlation
Method of studying Correlation Graphic Algebraic
1.Karl Pearson 2.Rank method 3.Concurrent Deviation Scatter Diagram Method
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demonstrate correlation betw een tw o quantitative variables.
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Scatter Plots of Data w ith Various Correlation Coefficients
Y X Y X Y X Y X Y X
r = -1 r = -Ve r = 0 r = +Ve r = 1
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negative linear relationship
positive linear relationship
positive linear relationship
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The value of r lies betw een - 1 and +1
between the variables
positive relationship between the variables .
negative relationship between the variables
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positive relationship between the variables .
negative relationship between the variables.
relationship between the variables
relationship between the variables .
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(X n,Y n) relating to tw o variables X and Y ,the Covariance of X and Y is usually represented by Cov(X,Y)
N xy N Y Y X X Y X Cov
= − − = . ) , (
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Properties of Co-Variance
Scale.
infinity to positive infinity.
be positive or negative or Zero.
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From the follow ing Data Calculate Co-Variance
X 1 2 3 4 5 Y 10 20 30 50 40
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X X-X=x Y Y-Y=y x.y 1 2 3 4 5
1 2 10 20 30 50 40
20 10 40 10 20 20 =15 =0 =150 =0 =90
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3 5 15 = = = ∑ N X X
30 5 150 = = = ∑ N Y Y
18 5 90 . ) , ( = = = − − =
N xy N Y Y X X Y X Cov
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mathematical method for measuring the intensity or the magnitude of linear relationship betw een tw o variables w as suggested by Karl Pearson's
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linear relationship betw een tw o quantitative variables
1 2 2 1 1 n i i i n n i i i i
X X Y Y r X X Y Y
= = =
− − = − −
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Properties of KralPear son’s Coefficient of Correlation
Measurement
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Assumptions of Karl Pearson’s Coefficient of Correlation
variables.
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lies betw een -1 and +1
is the geometric mean of tw o regression coefficients.
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Merits of Karl Pear son’s Coefficient of Correlation
direction as well as degree of relationship between variables
with other information helps in estimating the value of the dependent variable from the known value of independent variable.
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Limitations of KralPear son’s Coefficient of Correlation
Relationship
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From the follow ing Data Calculate Coefficient of correlation
X 1 2 3 4 5 Y 10 20 30 50 40
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X X-X=x x2 1 2 3 4 5
1 2 4 1 1 4 =15 =0 =10
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Y Y-Y=y y2 x.y 10 20 30 50 40
20 10 400 100 400 100 40 10 20 20 =150 =0 =1000 =90
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correlation
3 5 15 = = = ∑ N X X
30 5 150 = = = ∑ N Y Y
9 . 100 90 10000 90
2 2
+ = = = × =
y x xy r
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Correlation for Bivariate analysis ( )(
) ( ) ( )
− − − = N dx f d f N dx f d f N d f d f d fd r
y x y x y x 2 2 2 2
. . . . . . .
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Standard error
correlation is used foe ascertaining the probable error of coefficient of correlation
N r SE
2
1− =
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if added to and subtracted from value of r gives the upper and low er limits w ith in w hich coefficients of correlation in the population can be expected to lie. It is 0.6745 times of standard error.
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2
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Uses of Probable Error
reliability of the value of r in so far as it depends on the condition of random sampling.
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Case Interpretation 1.If |r |< 6 PE
The value of r is not at all significant. There is no evidence of correlation. The value of r is
evidence of correlation
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Error ,b) Probable Error and C) Limits of Population correlation .Also State whether r is significant
06 . 6 36 . 6 64 . 1 36 ) 8 . ( 1 1
2 2
= = − = − − = − = N r SE
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Error=0.6745.SE=0.6745* 0.06=0.04
times the Probable error ,the value of r is significant .Hence the existence of correlation
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Coefficient of determination
is defined as the ratio of the explained variance to the total variance
determination is calculated by squaring the coefficient of correlation
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variation in the dependent variable w hich is explained the independent variable?
dependent variable explained by independent variable.
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Coefficient of non-determination
determination is defined as the ratio of the unexplained variance to the total variance
determination is calculated by subtracting the Coefficient of determination from one.
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variation in the dependent variable w hich is not explained the independent variable?
=r2=0.64
the dependent variable not explained by independent variable.
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Spearman’s Rank Correlation
Spearman’s Rank Correlation uses
ranks than actual observations and make no assumptions about the population from which actual
2 2
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Spearman’s Rank Correlation for repeated ranks
are repeated
1 ..... 12 6 1
2 3 2
− + − + − =
n n m m D r
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Calculation of Rank Correlation
contest ranked the entries as follow s
X 1 2 3 4 5 Y 5 4 3 2 1
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X Y d=r1-r2 1 5
16 2 4
4 3 3 4 2 2 4 5 1 4 16 n=5 =40
2
d
∑
2
d
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2 2 2
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Features of Spearman’s Rank Correlation
coefficient is based on ranks rather than actual observations .
coefficient is distribution –free and non-parametric because no strict assumptions are made about the form of population from w hich sample observation are draw n.
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Features of Spearman’s Rank Correlation
ranks betw een tw o variables shall be Zero
Pearson’s Coefficient of Correlation.
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Merits of Spearman’s Rank Correlation
easy to apply
data.
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Limitations of Spearman’s Rank Correlation
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When is used Spearman’s Rank Correlation method
not know n
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Meaning of Concurrent Deviation Method
based on the direction of change in the two paired variables .The coefficient of Concurrent Deviation between two series of direction of change is called coefficient of Concurrent Deviation .
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the change direction of change of X- series and Y-Series
c
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Limitations of Concurrent Deviation Method
differentiate betw een small and big changes .
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Merits of Concurrent Deviation
calculate.
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Calculation of coefficient of concurrent deviation
X 59 69 39 49 29 Y 79 69 59 49 39
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X Direction
Y Direction
Change
Dx* Dy 59 69 39 49 29 +
69 59 49 39
n=4 C=2
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c
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association between two or more variables (a) coefficient of correlation (b) coefficient of regression (c) both (d) none of these
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association between two or more variables (a) coefficient of correlation (b) coefficient of regression (c) both (d) none of these
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between (a) –1 and +1 (b) 0 and +1 (c) –1 and 0 (d) none of these
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between (a) –1 and +1 (b) 0 and +1 (c) –1 and 0 (d) none of these
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(a) choice of origin and not of choice of scale (b) choice of scale and not of choice of
(c) both choice of origin and choice of scale (d) none of these
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(a) choice of origin and not of choice of scale (b) choice of scale and not of choice of
(c) both choice of origin and choice of scale (d) none of these
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(a) 0.6475 standard error (b) 0.6745 standard error (c) 0.6457 standard error (d) 0.6547 standard error
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(a) 0.6475 standard error (b) 0.6745 standard error (c) 0.6457 standard error (d) 0.6547 standard error
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is obtained by the formula (a) r = (b) r = (c) r = (d) r =
Y X N XY σ σ
y x N xy σ σ
y x N xy σ σ
y x N xy σ σ
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coefficient is obtained by the formula (a) r = (b) r = (c) r = (d) r =
Y X N XY σ σ
y x N xy σ σ
y x N xy σ σ
y x N xy σ σ
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Temperature and Sale of Woolen Garments.
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Temperature and Sale of Woolen Garments.
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defined from
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defined from
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0.36 ,the value of r will be
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0.36 ,the value of r will be
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variables
variables
variables having no causal relation
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variables
variables
variables having no causal relation
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developed by
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developed by
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situation is 0.49.what is the coefficient
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situation is 0.49.what is the coefficient
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correlation between variables .
correlation
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correlation between variables .
correlation
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determination is
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determination is
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variables x and y is given by 2x + 3y + 4 = 0, then the value of the correlation coefficient between x and y is
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variables x and y is given by 2x + 3y + 4 = 0, then the value of the correlation coefficient between x and y is
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about beauty between two Judges in a Beauty Contest, we use______ .
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about beauty between two Judges in a Beauty Contest, we use______ .
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defined as
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defined as
Correla latio ion