R Tutorial : Features of your measure: Correlations and reliability

Want to learn more? Take the full course at https://learn.datacamp.com/courses/factor-analysis-in-r at your own pace. More than a video, you'll learn hands-on coding & quickly apply skills to your daily work. --- By this point, you've looked at basic descriptive statistics of your dataset and learned how to split the data into random halves. When writing a description of your measure, you'll also want to include some more detailed information. Correlations are the standard way of reporting relationships between variables. The lowerCor() function provides this data in a more reader-friendly format than base R's cor() function. The diagonal of ones represents the perfect correlation between each item and itself, and the other values are the correlations between each pair of items. lowerCor() displays only the lower triangle of the correlation matrix, so each pair's correlation is only displayed once. This correlation matrix is your first clue about factor structure. Groups of items that are more strongly correlated typically load onto the same factor. Once you've used lowerCor() to find the correlations between items, you will likely also want to report their significance and confidence intervals. corr.test() can be used to generate both of these metrics for inter-item correlations. corr.test() generates a lot of output when you run it, and results are given as a full matrix instead of just the lower half like lowerCor(). Its result object is a list, so you can specify named list elements to get only the information you want to view. In this example, we are accessing the 'p' list element to get the p-values for each of the correlations. This slide displays the p-values for the correlations of the items. All those zeroes indicate statistically significant correlations. This is unsurprising given that the gcbs dataset has over 2,000 cases since statistical significance is affected by sample size. You can also use corr.test() to view confidence intervals for ea