A decision table is a specification-based test technique that involves creating a table that shows the combinations of inputs and outputs for a system under test based on certain conditions and rules. A decision table can be used to design test cases that cover all possible scenarios and outcomes for a system under test. Some statements about decision tables are:

I. Generally, decision tables are generated for low risk test items: This statement is false because decision tables can be generated for any level of risk test items depending on the complexity and variability of the system under test. Decision tables are especially useful for testing systems that have many inputs, outputs, conditions, and rules that affect their behavior or performance.

II. Test cases derived from decision tables can be used for component tests: This statement is true because decision tables can be used to design test cases for any level or type of testing, including component tests. Component tests are tests that verify individual components or units of software in isolation from other components or systems.

III. Several test cases can be selected for each column of the decision table: This statement is true because each column of the decision table represents a unique combination of inputs and outputs for the system under test based on certain conditions and rules. Therefore, each column can be used as a basis for selecting one or more test cases that cover that combination.

IV. The conditions in the decision table represent negative tests generally: This statement is false because the conditions in the decision table can represent both positive and negative tests depending on the requirements and expectations of the system under test. Positive tests are tests that verify that the system under test behaves as expected under valid or normal inputs or conditions. Negative tests are tests that verify that the system under test handles errors or exceptions gracefully under invalid or abnormal inputs or conditions.

You can find more information about decision tables in [A Study Guide to the ISTQB® Foundation Level 2018 Syllabus], Chapter 4, Section 4.2.