Final answer:
Two potential threats to internal validity are lurking variables and the lack of blinding. Lurking variables can offer alternative explanations for an observed effect, while the lack of blinding can lead to biased results influenced by participant or researcher expectations.
Step-by-step explanation:
The two potential threats to internal validity are lurking variables and the lack of blinding. Lurking variables are extraneous factors that can affect the outcome of a study without being directly measured. These uncontrolled variables can provide alternative explanations for any observed effects, thereby threatening the integrity of the experimental conclusions. To mitigate this threat, researchers should aim to identify and control for any potential lurking variables.
Blinding is a method used to prevent bias in research, where study participants, and sometimes researchers, are kept unaware of critical aspects of the experiment, such as which participants are receiving the treatment and which are receiving a placebo. The use of blinding can help ensure that the treatment effects are not influenced by participants' or experimenters' expectations. In studies where blinding is not possible, the interpretation of the results may be confounded by bias.