To remember the difference between these two terms, pay attention to the last three letters.  is the same as attribute Principle is a noun that means basic truth, law, rule, or assumption. Eigenvectors and eigenvalues are the linear algebra concepts that we need to compute from the covariance matrix in order to determine the principal components of the data. To put all this simply, just think of principal components as new axes that provide the best angle to see and evaluate the data, so that the differences between the observations are better visible. Some of the most frequently-used of those definitions are: As an adjective, the word means first, or highest in rank. Organizing information in principal components this way, will allow you to reduce dimensionality without losing much information, and this by discarding the components with low information and considering the remaining components as your new variables. The second principal component is calculated in the same way, with the condition that it is uncorrelated with (i.e., perpendicular to) the first principal component and that it accounts for the next highest variance. Also, keep in mind that principle is always a noun and will never be used as an adjective. So, transforming the data to comparable scales can prevent this problem. Principal can also be turned into the adverb principally, meaning “for the most part.” If you were principally a children’s book author, it would mean you primarily wrote children’s books, but might venture into other genres or have a side-career. For the Sexual and Reproductive Health Activity Data Set the CONTRACEPTION PRINCIPAL METHOD is the principal method of CONTRACEPTION provided to a PATIENT at a Sexual and Reproductive Health Clinic attendance (or the PATIENT is maintaining under the service's care) where an intervention to the principal method of CONTRACEPTION occurs. PATIENT If you consider yourself a law-abiding person, you would not call yourself a principle. contraception principal method For the Sexual and Reproductive Health Activity Data Set the CONTRACEPTION PRINCIPAL METHOD is the principal method of CONTRACEPTION provided to a PATIENT at a Sexual and Reproductive Health Clinic attendance (or the PATIENT is maintaining under the service's care) where an intervention to the principal method of CONTRACEPTION occurs. It’s actually the sign of the covariance that matters : Now, that we know that the covariance matrix is not more than a table that summaries the correlations between all the possible pairs of variables, let’s move to the next step.