ABSITE statistics: the absolute basics

Christian Jones, MD, FACSDepartment of Surgery

Johns Hopkins School of Medicine

statsO mean: typical “average”O median: middle numberO mode: most frequent numberO normal: type of distribution, equal about a

mean, “bell curve”, mean = median = mode

termsO incidence: interval of timeO prevalence: point in time

types of studiesO cohort study: prospective, nonrandom

assignment to treatment groupO case-control study: retrospective,

nonrandom

biasesO selection bias: test groups end up being

different, e.g., volunteers vs. populationO measurement bias: aka system bias, actual

measurement is inaccurate, e.g., recall biasO exposure bias: aka treatment bias,

treatments not applied equally or as originally planned, e.g., dead patients “withdraw”

test parametersO sensitivity: how well does the test see the

disease?O specificity: how well does the test make sure

it really is the disease?O positive predictive value: if the test says yes,

how certain can you be that it’s right?O negative predictive value: if the test says no,

how certain can you be that it’s right?

copyright, etc.This document is entirely the work of Christian Jones (on-call@christianjones.md) and is hereby released into the public domain, with no rights reserved.

This is version 1.1, last modified on 28 January 2016 by Christian Jones. Contact the author by email or on Twitter (@jonessurgery) for questions, comments, or concerns.