Graphic Methods

a.Scatter Diagram: Scatter  diagram  is a special  type of dot chart.  Under  this methods  the given data are  plotted in  a graph  paper  in the form of  dot. For each  pair of  or x and y values  we plot a dot( or  point) and thus  we obtain  many  dots equal in number of observation. If now these  plotted dotes  or points  show some  trends  either  upwards or downwards then the two variables  ( x and y) are said to  be correlated or otherwise not correlated. If  again  the trend of points  is upwards  moving  from  lower left hand corner to upper right hand corner then correlation is positive  ( r=+1) r is  coefficient  or correlation. On the  other hand if movement is reverse i, e,  dots  move  from  upper  left hand  corner  to lower right  hand corner then correlation  is negative (r= -1). The  idea  will be  clear from  diagram given  below:

                    Positive Correlation                    Negative  Correlation

In fig (a) the values  of the two  variable  move in the same  direction the correlation is  positive and r= 1.

 In figure (b) we  find  negative  correlation and r= 1 as the values  move in  reverse direction.

 In figures (c) we dont  get any  trend  lying  and heance it shows  the  absence  of correlation  and r= 0.