Recall the chapter on research methods in your text. natural improvement, nonspecific treatment effects, and placebo effects are best seen as threats to the of outcome research.

Internal validity.

Explanation:

Internal validity is the study in which trust relationship is build between treatment and outcome. This relationship is known as cause-and-effect.

In this type research, the studies are based on whether the finding is questionable or not. The research which can overrule the possibility of alternative explanations of our findings is internally valid.

The threats of internal valid study are:

So, the correct answer is 'Internal validity'.

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the federal government of the united states was established by the constitution. us is a presidential republic. the president is head of state, head of government and of a two party legislative and electoral system. the supreme court balances the powers of the federal and the state government. yhe executive branch is headed by the oresident. there are two chambers of congress, the senate and the house of representatives. judicial power is exercised by the judicial branch (or judiciary), comprised of the supreme court and lower federal courts. the judiciary's function is to interpret the   constitution as well as the federal laws and regulations.