G544 Sec A Exam Talk. Variables IV, DV, extraneous variables. Type 1 and type 2 errors. What is the standard deviation? 7 key facts about science. How to choose a statistical test. Measures of central tendency mean, median and mode. How to write hypotheses. Hypothesis tests, p-value - Statistics Help. Types of Data: Nominal, Ordinal, Interval/Ratio - Statistics Help.