Data considerations for Correlogram

The data must include at least two columns of numeric data
The columns must have the same number of rows. You cannot include any columns with text or date/time data.
The data should be continuous or ordinal
If you have categorical data, you should perform Cross Tabulation and Chi-Square to examine the association between variables.
The sample size should be not be small
Although there are no formal guidelines for the amount of data needed for a correlogram, larger samples more clearly indicate patterns in the data.
The sample data should be selected randomly
In statistics, random samples are used to make generalizations, or inferences, about a population. If your data were not collected randomly, your results may not represent the population.
The relationship between variables should be linear
If your variables do not have a linear relationship, the correlogram will not accurately reflect the strength of the relationship. Examine a matrix plot to look for other relationships.
Unusual values can have a strong effect on the results
Because unusual values can have a strong effect on the results, use a matrix plot to identify these values. You should investigate outliers because they can provide useful information about your data or process.