Path and Variance Covariance Analysis

Path analysis is an extension of the regression model, used to test the fit of the correlation matrix against two or more causal models which are being compared by the researcher. The model is usually depicted in a circle-and-arrow figure in which single arrows indicate causation. A regression is done for each variable in the model as a dependent on others which the model indicates are causes. The regression weights predicted by the model are compared with the observed correlation matrix for the variables, and a goodness-of-fit statistic is calculated. The best-fitting of two or more models is selected by the researcher as the best model for advancement of theory.

Data Arrangement in data file

• Un-replicated data (the data arrangement is same as that of correlation and regression Analysis)

• Correlation Matrix (Correlation matrix is entered in data file or text area of the web page.

• Replicated data : In this method the character under study are laid down horizontal and replication within treatments are laid down vertical i.e. first replication of first treatment of all the characters must be entered in first line and the observations are separated by space or tabs, enter second replication of first treatment of all the characters in second line. Similarly enter all the replications of first treatment of all the characters in separate lines. Now take the second treatment and enter all the replications in sub sequent lines.

Example : For 10 genotypes, 3 replication and 8 Characters the data arrangement is as under

(Let G₁,G₂,G₃, .... G₁₀ represents Genotypes, R₁,R₂ and R₃ represents replications and C₁,C₂,C₃, . . . C₈ represents the Characters under study)

Data Arrangement in a file or in text area of web page  is

              C₁      C₂     C₃     C₄     C₅      C₆       C₇        C₈

G₁R₁

G₁R₂

G₁R₃

G₂R₁

G₂R₂

G₂R₃

G₃R₁

G₃R₂

G₃R₃

G₄R₁

G₄R₂

G₄R₃

G₅R₁

G₅R₂

G₅R₃

G₆R₁

G₆R₂

G₆R₃

G₇R₁

G₇R₂

G₇R₃

G₈R₁

G₈R₂

G₈R₃

G₉R₁

G₉R₂

G₉R₃

G₁₀R₁

G₁₀R₂

G₁₀R₃

Procedure of Analysis

• Create data file and enter the data according to the above mentioned scheme.

• Click on Browse button, Select the  data file and  press Send button if data are stored in a file or enter/paste the data in  in the text area of the web page and press the Submit button.

• Enter the parameters required for analysis such as Total number of variables in data file, Number of treatments (This field is applicable only if  genotypic, phenotypic or Environmental Correlations are used in path Analysis), Observations per variable (applicable only if un-replicated data are used), Dependent variable number (here you have to enter the column no which belongs to dependent variable) and Independent variable numbers (type the independent variables in the text box separated by space)

• Choose the Path analysis option

• Select the statistics options

• Press Analyse button to analyse your data.