Variables Should Not Contain Multiple Variables (e.g., Comma-separated)

It's technically possible to create a single variable in a data file that actually contains multiple variables. When this occurs, it requires the person using the data to have to correct the problem, which is not trivial.

Commas separated values

The most common example of this is where a text variable contains comma-separated values, as in the example below. 

The remedy for a problem like this is to either create new variables by splitting this variable apart by comma or, to obtain a new data file.

Combining quantity and measurement unit

Another common example is to splice quantity and measurement unit into a single variable (e.g., 45KG, which ends up being a text variable, whereas it would be better to have the number stored as numeric, and the measurement unit as nominal.