Factors influencing reliability measures

1- Length of Test.
The longer the test is, the higher its reliability will be.
2- Spread of Scores.
The larger the spread of score is, the higher the estimate of reliability will be.
3- Difficulty of Test.
Too easy or too difficult tests have low reliability.
4- Objectivity.
The standardized tests which are high in objectivity, have high reliability.
5- The length of the test.
6- The time limits for the tests.
7- A common set of instructions.
8- The scoring procedure of the test.
9- A common environment in which to attempt the test.
10- The difficulty of the test items. (i.e., if the test items are too difficult than the spread of scores will be small).
11- The nature of the student group. (i.e., if the group is quite homogeneous the reliability will be lower than if the group is fairly heterogeneous).
12- Tests that are too easy.
13- Tests that are too hard.
14- The more questions the better reliability.
15- There is always a degree of error in any test score.