Factors Affecting Validity of a test.

Validity evidence is an important aspect to consider while thinking of the classroom testing and measurement. There are many factors that tend to make test result invalid for their intended use. A little careful effort by the test developer help to control these factors, but some of them need systematic approach. No teacher would think of measuring knowledge of social studies with an English test. Nor would a teacher consider measuring problem-solving skills in third-grade arithmetic with a test designed for sixth grades. In both instances, the test results would obviously be invalid. The factors influencing validity are of this same general but match more subtle in character. For example, a teacher may overload a social studies test with items concerning historical facts, and thus the scores are less valid as a measure of achievement in social studies. Or a third–grade teacher may select appropriate arithmetic problems for a test but use vocabulary in the problems and directions that only the better readers are able to understand. The arithmetic test then becomes, in part, reading test, which invalidates the result for their intended use. These examples show some of the more subtle factors influencing validity, for which the teacher should be alert, whether constructing classroom tests or selecting published tests. Some other factors that may affect the test validity are discussed as under.

1. Instructions to Take A Test:
The instructions with the test should be clear and understandable and it should be in simple language. Unclear instructions may restrict the pupil how to respond to the items, whether it is permissible to guess, and how to record the answers will tend to reduce validity.
2. Difficult Language Structure:
Language of the test or instructions to the test that is too complicated for the pupils taking the test will result in the test’s measuring reading comprehension and aspects of intelligence, which will distort the meaning of the test results. Therefore it should be simple considering the grade for which the test is meant.
3. Inappropriate Level of Difficulty:
norm-references tests, items that are too easy or too difficult will not provide reliable discriminations among pupils and will therefore lower validity. In criterion-referenced tests, the failure to match the difficulty specified by the learning outcome will lower validity.
4. Poorly Constructed Test Items:
There may be some items that provide direction to the answer or test items that unintentionally provide alertness in detecting clues are poor items, these items may harm the validity of the test.
5. Ambiguity in Items Statements:
Ambiguous statements in test items contribute to misinterpretations and confusion. Ambiguity sometimes confuses the better pupils more than it does the poor pupils, causing the items to discriminate in a negative direction.
6. Length of the Test:
A test is only a Sample of the many questions that might be asked. If a test is too short to provide a representative sample of the performance we are interested in, its validity will suffer accordingly. Similarly a too lengthy test is also a threat to the validity evidence of the test.
7. Improper Arrangement of Items:
Test items are typically arranged in order of difficulty, with the easiest items first. Placing difficult items early in the test may cause pupils to spend too much time on these and prevent them from reaching items they could easily answer. Improper arrangement may also influence validity by having a detrimental effect on pupil motivation. The influence is likely to be strongest with young pupils.
8. Identifiable Pattern of Answers:
Placing correct answers in some systematic pattern will enable pupils to guess the answers to some items more easily, and this will lower validity.
In short, any defect in the tests construction that prevents the test items from functioning as intended will invalidate the interpretations to be drawn from the results. There may be many other factors that can also affect the validity of the test to some extents. Some of these factors are listed as under.
 Inadequate sample
 Inappropriate selection of constructs or measures.
 Items that do not function as intended
 Improper administration: inadequate time allowed, poorly controlled conditions
 Scoring that is subjective
 Insufficient data collected to make valid conclusions.
 Too great a variation in data (can't see the wood for the trees).
 Inadequate selection of target subjects.
 Complex interaction across constructs.
 Subjects giving biased answers or trying to guess what they should say.