Q: What is a type I error and a type II error in bio-statistics? 


Answer:  Proper design is the core to any credible medical study

Type I error (alpha error) is incorrectly concluding that there is a statistically significant difference in collected data - making statistically insignificant conclusion significant. In other words, incorrect rejection of a true null hypothesis.

Type II error (beta error) is incorrectly concluding that there was no statistically significant difference in collected data - making statistically significant conclusion insignificant. In other words,  failure to reject a false null hypothesis.