Final answer:
The correct answer is b. External validity. Random sampling increases external validity of a study because it ensures that every individual in the population has an equal chance of being selected, making the results generalizable to the larger population.
Step-by-step explanation:
The correct answer to the question 'A randomly selected sample increases the likelihood that experimental results will generalize to the population. In other words, a random sample increases ______ validity.' is b. External validity. External validity refers to the extent to which the results of a study can be generalized or extended to others outside the sample used in the study. Random sampling, which gives every individual in the population an equal chance of being selected, enhances external validity because it increases the odds that the sample represents the broader population.
Choosing a random sample is effective because d. everyone has the same chance of being part of the study. This reduces bias and increases the likelihood that the sample is representative of the larger population. Reliability of a study is about consistency of results, while validity assesses how well the study measures what it is supposed to measure. When research incorporates random sampling, these attributes are better upheld, enhancing the validity and credibility of the research findings.