UGC NET Questions (Paper – 1)

Statements A, B, C, D and F correctly describe threats to internal validity, while E is false. Statement A is true because events between measurements can influence outcomes. Statement B is correct as maturation refers to participant changes over time, and statement C rightly defines the testing effect. Statement D accurately explains instrumentation changes, and statement F is true for attrition or mortality, whereas E is false because random assignment is a control technique that strengthens, not threatens, internal validity.

Option A:
Option A includes all the genuine threats named (A, B, C, D and F) and excludes E, which misinterprets the role of random assignment. It thus presents a complete and accurate set of internal validity threats mentioned in the list. Therefore this option is the correct answer.

Option B:
Option B leaves out F, ignoring the issue of differential dropout across groups. Since attrition can seriously bias results, omitting it gives an incomplete picture of internal validity threats. As a result, this combination is not acceptable.

Option C:
Option C contains E in addition to B, C, D and F, thereby treating random assignment as a threat. This is incorrect because random assignment is used to control extraneous variables and enhance internal validity. Including a false statement disqualifies this option.

Option D:
Option D omits B, which is an important threat related to participant changes, and therefore fails to recognise the full range of threats in the list. By leaving out a true statement, it offers only a partial account and cannot be considered correct.

Statement E is the only wrong statement because random assignment actually strengthens internal validity by equalising groups on extraneous variables. History, maturation, testing and instrumentation are all recognised threats that can introduce alternative explanations for observed changes if not controlled. Thus, A, B, C and D accurately name and describe typical threats, while E reverses the protective role of random assignment.

Option A:
Option A is incorrect because it groups A with E as wrong, even though A correctly defines history as external events occurring during the study period. Misclassifying A undermines the standard taxonomy of threats.

Option B:
Option B is also wrong because it treats B along with E as incorrect, even though B adequately describes maturation as internal changes over time. Including B among wrong statements disrupts the understanding of developmental influences on participants.

Option C:
Option C is correct because it isolates E, the statement that conflicts with experimental logic, and implicitly affirms the accuracy of A, B, C and D. It recognises that random assignment is a remedy, not a threat.

Option D:
Option D is incorrect because it pairs C with E, even though C correctly identifies testing effects. By labelling C as wrong, this option denies a well-acknowledged validity threat.

Systematic error is a form of measurement error that biases results in a consistent direction, such as always overestimating or underestimating the true value. Unlike random error, it does not average out over repeated measurements and therefore threatens the validity of conclusions. It often arises from faulty instruments, biased procedures or consistent miscalibration. Because the stem describes a consistent tendency to give values higher or lower than the true value, systematic error is the correct term.

Option A:
Random error arises from unpredictable fluctuations in measurement conditions, leading to variations that cancel out over many observations and primarily affect reliability rather than bias. It does not consistently push measurements in one direction, so random error does not match the description in the stem.

Option B:
Sampling error refers to the difference between sample statistics and population parameters that occurs because only a subset of the population is observed. It is related to sample selection rather than to the behaviour of measuring instruments. Therefore, sampling error is not the right completion here.

Option C:
Systematic error is problematic because it can lead to false conclusions even when large samples are used and results appear stable. Researchers must identify and correct sources of systematic bias to preserve validity. These characteristics correspond directly to the stem, confirming systematic error as the appropriate answer.

Option D:
Estimation error is a broader term referring to discrepancies between estimated and true values, which may result from both systematic and random components. The stem, however, specifically focuses on a consistent directional bias, so the more precise term systematic error is preferable.