Answer:
a). threats to external validity are decreased by carefully controlling conditions
Explanation:
Validity in a research work represents whether the conclusion or the results of the study correct and meaningful. External validity may be defined as how the findings of the research are applicable to the real world.
It is the validity of relating the results of a scientific study outside the conditions of that particular study.
There are seven important factors that affects the external validity. They are :
1. time effect
2. effects of the experimenter
3. research environment effect
4. subjects
5. Descriptive explicitness
6. Interaction between research and subject
7. Method of data collection
By controlling these conditions, the threat to external validity can be decreased.
Hence the answer is ----
a). threats to external validity are decreased by carefully controlling conditions