Advantages of Multivariate Analysis

# Advantages of Multivariate Analysis

Télécharger la présentation

## Advantages of Multivariate Analysis

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
##### Presentation Transcript

1. Advantages of Multivariate Analysis • Close resemblance to how the researcher thinks. • Easy visualisation and interpretation of data. • More information is analysed simultaneously, giving greater power. • Relationship between variables is understood better. • Focus shifts from individual factors taken singly to relationship among variables.

2. Definitions - I • Independent (or Explanatory or Predictor) variable always on the X axis. • Dependent (or Outcome or Response) variable always on the Y axis. • In OBSERVATIONAL studies researcher observes the effects of explanatory variables on outcome. • In INTERVENTION studies researcher manipulates explanatory variable (e.g. dose of drug) to influence outcome

3. Definitions - II • Scatter plot helps to visualise the relationship between two variables. • The figure shows a scatter plot with a regression line. For a given value of X there is a spread of Y values. The regression line represents the mean values of Y.

4. Definitions - III • INTERCEPT is the value of Y for X = 0. It denotes the point where the regression line meets the Y axis • SLOPE is a measure of the change in the value of Y for a unit change in X. Y axis Slope Intercept X axis

5. Basic Assumptions • Y increases or decreases linearly with increase or decrease in X. • For any given value of X the values of Y are distributed Normally. • Variance of Y at any given value of X is the same for all value of X. • The deviations in any one value of Y has no effect on other values of Y for any given X

6. The Residuals • The difference between the observed value of Y and the value on the regression line (Fitted value) is the residual. • The statistical programme minimizes the sum of the squares of the residuals. In a Good Fit the data points are all crowded around the regression line. Residual

7. Analysis of Variance - I • The variation of Y values around the regression line is a measure of how X and Y relate to each other. • Method of quantifying the variation is by Analysis of variance presented as Analysis of Variance table • Total sum of squares represents total variation of Y values around their mean - Syy

8. Analysis of Variance - II Total Sum of Squares ( Syy ) is made up of two parts: (i). Explained by the regression (ii). Residual Sum of Squares Sum of Squares ÷ its degree of freedom = Mean Sum of Squares (MSS) The ratio MSS due to regression ÷ MSS Residual = F ratio

9. Reading the output • Regression Equation • Residual Sum of Squares (RSS) • Values of α and β. • R2 • S (standard deviation) • Testing for β≠ 0 • Analysis of Variance Table • F test • Outliers • Remote from the rest