3 Data collection

• Sample data should be always organized in matrix form, with observations presented in rows and variables in columns, and saved in a file format such as .xlsx, .txt or .csv

• Most common data issues:

1. Missing values (NA)
2. Measurement errors (collected data may not always present true values)
3. Outliers (extreme values above or below the mean)

• Raw data are usually transformed:

1. Taking the logs, squares, inverse values, square roots, …
2. Seasonally and/or calendar adjusted
3. First differences are sometimes required as well as lagged values
4. Deflating nominal values