# PNB 3RM3 Lecture Notes - Lecture 31: Statistical Inference, Variance, Descriptive Statistics

## Document Summary

Descriptive statistics variability and z scores variability of a sample: Correct for the bias with a minor adjustment: Sample variance tends to be an underestimation of the variability of the population. Sample variance gives us an artificial sense of what the variability in the population actually is. Correct for this bias with a minor adjustment (subtract 1 from the sample size (n) ) Denominator will get a bit smaller resulting in the product of division to get slightly if you are making an inference about a population, you will always have this adjustment larger percentiles: Percentile rank of a score: percentage of scores in the distribution that are lower than that score. Ex: 80th percentile = 80% of the population has an iq lower than you. Need to measure cumulative frequency add all frequencies in the column above and including the row you are finding the cf for: ex. Cf of row 2: 1 + 2 = 3, 1+2+2= 5.