Sumukh Deshpande n Lecturer College of Applied Medical Sciences Statistics = Skills for life. BIOSTATISTICS (BST 211) Lecture 2

Basic Data Analysis Process in Descriptive Statistics

 Is the data set a sample? Basic Data Analysis Process in Descriptive Statistics Yes RAW DATA "Filtered" DATA Nominal/Ordinal/Interval Range & Rank Data Is the data parametric ? No Sample/Population? N or n? s or  ? xbar or  ? Inspection: Outliers/missing values/other abnormalities SizeMeanSD Sample nX bars Population N 

 The odd ones out  Observations that are too large or too small.. (e.g a child 777cm tall)  They may be genuine!  Typing errors?  Other errors?  What should you do? Outliers 1 Yes RAW DATA "Filtered" DATA Nominal/Ordinal/Interval Range & Rank Data Is the data parametric ? No Sample/Population? N or n? s or  ? xbar or  ? Inspection: Outliers/missing values/other abnormalities

 Make note of outliers  Repeat analysis with and without outliers to show the difference  MISSING data is to be reported and investigated Outliers 2 Yes RAW DATA "Filtered" DATA Nominal/Ordinal/Interval Range & Rank Data Is the data parametric ? No Sample/Population? N or n? s or  ? xbar or  ? Inspection: Outliers/missing values/other abnormalities

 Before you perform analysis you must be comfortable with your data  Never remove outliers or add in missing data!  Assess and report. DO NOT ALTER RAW DATA “Filtered” Data Yes RAW DATA "Filtered" DATA Nominal/Ordinal/Interval Range & Rank Data Is the data parametric ? No Sample/Population? N or n? s or  ? xbar or  ? Inspection: Outliers/missing values/other abnormalities

Discrete Data

 Count your data. Check the size. N or n?  Rank the data min →Max or vice-versa  Work out the range Sorting your Data Yes RAW DATA "Filtered" DATA Nominal/Ordinal/Interval Range & Rank Data Is the data parametric ? No Sample/Population? N or n? s or  ? xbar or  ? Inspection: Outliers/missing values/other abnormalities Go to Excel ®

Ex1: KKH patients, 5 weeks  Is this data discrete or continuous? Week Week Week Week Week Why are these columns different?  Any outliers? Or missing data?

Ex2: school kids height  Is this data discrete or continuous?  Any outliers? Or missing data?

Ranking your Data using MS Excel  Put your data in ONE column, then select it all. Press

Frequency Tables & Charts

Frequency Tables 1 1. Rank your Data 2. Count how many times each observation appears 3. You have just made a FREQUENCY Table Xf Xf

Charts Using Excel 1. Charts help visualise data 2. Summarise information and facts 3. Easy to create with Excel 1. Charts are created from frequency tables 2. How to create a chart? 3. m/watch?v=jLW1A7j7 r3Y m/watch?v=jLW1A7j7 r3Y

Chart of the previous example Xf

Calculating Statistical Functions using MS Excel & Calculators Discrete Data

Stats functions Using Excel 1. Mean: =average(data range) 2. Median: =median(data range) 3. Mode: =mode(data range) 1. SD: =stdev(data range) 2. edu/~otorres/Excel/e xcelstata.htm edu/~otorres/Excel/e xcelstata.htm

1. First go to SD mode 2. Clear memory 3. Enter data CORRECTLY 4. Visualise your data 5. Retrieve Statistical Functions Stats functions Using Casio fx-8nMS

1. Selecting SD Mode

2. Deleting Previous stats in memory

3. Entering Data

4. Visualising Data

5. Retrieve Statistical Function

Practice Example  Calculate descriptive stats functions of the following data set using calculators, MS Excel and long hand calculation 55, 54, 51, 55, 53, 53, 54, Start with long hand 2. Then Calculator 3. Finally use Excel

1. Long Hand 1. Freq Table Mean, xbar = 427/8 = n = Variance = /(8-1)=1.98 SD =  Variance =  1.98 = , 54, 51, 55, 53, 53, 54, 52

2. Calculator 55, 54, 51, 55, 53, 53, 54, 52

3. Excel 55, 54, 51, 55, 53, 53, 54, 52

All 3 routes led to the same answers Long Hand CalculatorExcel Mean53.38 SD1.41