Statistics Idiots Guide

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Statistics Idiots Guide!

• Dr. Hamda Qotba, B.Med.Sc, M.D, ABCM

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Definition
Statistics is the science of collecting,
organizing, summarising, analysing, and making
inference from data
Descriptive stat. Includes collecting,
organizing, summarising, analysing, and
presenting data
Inferential stat. Includes Making inferences,
hypothesis testing Determining relationship,
and making prediction
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Variables

• Quantitative
• Discrete
• Continuous

• Qualitative
• Ordinal
• Categorical

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Parametric Vs.
non parametric tests

• Parametric decision making method where the
  distribution of the sampling statistic is known
• Non-Parametric decision making method which does
  not require knowledge of the distribution of the
  sampling statistic

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t-Test

• Compare the means of a continuous variable into
  samples in order to determine whether or not the
  difference between the 2 expected means exceed
  the difference that would be expected by chance

What is probability the mean will differ?
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• Requirements
• The observations are independent
• Drawn from normally distributed population
• Sample size lt 30 if its gt30 use normal curve z
  test (binomial test)

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Types of t-Test

• One sample t test test if a sample mean for a
  variable differs significantly from the given
  population with a known mean
• Unpaired or independent t test test if the
  population means estimated by independent 2
  samples differ significantly (group of male and
  group of female)
• Paired t test test if the population means
  estimated by dependent samples differ
  significantly (mean of pre and post treatment
  for same set of patients

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chi² test

• Used to test strength of association between
  qualitative variables
• Used for categorical data

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Requirements

• Data should be in form of frequency
• Total number of observed must exceed 20
• Expected frequency in one category or in any cell
  must be gt5 (When 1 of the cells have lt5 in
  observed yats correction) or if (When 1 of the
  cells have lt5 in expected fischer exact)
• The group compared must be approximately the same

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Correlation and Regression

• Methods to study magnitude of the association and
  the functional relationship between two or more
  variables

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Correlation

• Denote strength of relationship between variables

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Regression

• Method thats indicate a mathematical
  relationship between a dependant and one or more
  independent variables
• Simple linear regression and multiple regression
  are appropriate for continuous variables like(BP,
  Weight)
• Logistic regression applicable for binary
  response like alive/dead

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Measures

• If parametric
• Pearson correlation coeff.
• Continuous variables
• Linear relationship
• If nonparametric
• Spearman rank
• Both variables are continuous
• Kendalls tau
• Two ordinal or one ordinal one continuous

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ANOVA

• is used to uncover the main and interaction
  effects of categorical independent variables
  (called "factors") on an interval dependent
  variable

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Types of ANOVA

• One-way ANOVA tests differences in a single
  interval dependent variable among two, three, or
  more groups formed by the categories of a single
  categorical independent variable.

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• Two-way ANOVA analyzes one interval dependent in
  terms of the categories (groups) formed by two
  independents, one of which may be conceived as a
  control variable
• Multivariate or n-way ANOVA. To generalize, n-way
  ANOVA deals with n independents. It should be
  noted that as the number of independents
  increases, the number of potential interactions
  proliferates

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How to select appropriate statistical test

• Type of variables
• Quantitative (blood pres.)
• Qualitative (gender)
• Type of research question
• Association
• Comparison
• Risk factor
• Data structure
• Independent
• Paired
• matched

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Body of research question Association of 2
variable(dep, indep)
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Comparing (difference) variables
Number of independent variable 2
groups paired data gt2groups
Variable
Quantitative Ordinal Categorical
T test
Paired T test
ANOVA
Kruskal wallis
Mann-Whitney
Wilcoxon
chi-square
chi-square
McNemar
When 1 of the cells have lt5 in expected
fischer exact When 1 of the cells have lt5 in
observed yats correction
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Looking for Risk Factor