Internal consistency of collected data refers to the degree to which the data is reliable and consistent within itself. It can be checked by comparing two or more related series of data. Option D is the correct answer because it mentions the comparison of a number of related series, which is the most effective way to check for internal consistency.

Explanation:

To understand the concept of internal consistency, consider the following example. Suppose a company has collected data on the sales of its products for the past three years. If the data is internally consistent, it should show a logical pattern of increase or decrease over the three years. In other words, the data should be reliable, and there should not be any random variations that cannot be explained.

The following points explain how the internal consistency of collected data can be checked:

1. Compare related series: To check the internal consistency of collected data, it is essential to compare two or more related series of data. For instance, if the company has collected data on the sales of its products, it can compare the sales figures of different products or different regions over the same period to check for consistency.

2. Check for outliers: Outliers refer to data points that are significantly different from other data points. Outliers can affect the internal consistency of the data. Hence, it is essential to identify and remove outliers from the data.

3. Use statistical tests: Statistical tests can help in checking the internal consistency of collected data. For example, correlation analysis can be used to determine the degree of association between two variables, and regression analysis can be used to predict the value of one variable based on the value of another variable.

4. Check for missing data: Missing data can also affect the internal consistency of collected data. Hence, it is essential to check for missing data and take appropriate steps to fill in the missing values.

Conclusion:

In conclusion, the internal consistency of collected data is crucial to ensure its reliability and accuracy. Comparing two or more related series of data is the most effective way to check for internal consistency. By following the above-mentioned points, one can ensure that the collected data is internally consistent and reliable.