Sumukh Deshpanden

LecturerCollege 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

Size Mean SDSample n X bar s

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

Make note of outliers Repeat analysis with

and without outliers to show the difference

MISSING data is to be reported and investigated

Outliers 2

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

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

Go to Excel®

Ex1: KKH patients, 5 weeks

Is this data discrete or continuous?

Week 1 159 123 175 199 117 127 98 33Week 2 172 136 185 100 160 118 75 21Week 3 172 145 169 176 185 180 91 100Week 4 100 117 124 178 109 104 80 25Week 5 170 104 181 199 155 156 86 28

Why are these columns different? Any outliers? Or missing

data?

Ex2: school kids height Is this data discrete

or continuous?134 144 138 141 136 138 142 145

134 138 140 140 134 136 137

139 137 41 144 136 138 136 132

142 135 136 139 142 140 134 140

143 134 137 144 192 141 134 141 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 11. Rank your Data2. Count how many

times each observation appears

3. You have just made a FREQUENCY Table

X f

45 32 47 45 32 48 47 4745 48 51 47 32 51 45 48

X f32 345 447 448 351 2

16

Charts Using Excel1. Charts help

visualise data2. Summarise

information and facts

3. Easy to create with Excel

1. Charts are created from frequency tables

2. How to create a chart?

3. http://www.youtube.com/watch?v=jLW1A7j7r3Y

Chart of the previous example

X f32 345 447 448 351 2

Calculating Statistical Functions using MS Excel

& Calculators

Discrete Data

Stats functions Using Excel1. Mean:

=average(data range)

2. Median: =median(data range)

3. Mode: =mode(data range)

1. SD: =stdev(data range)

2. http://www.princeton.edu/~otorres/Excel/excelstata.htm

1. First go to SD mode2. Clear memory3. Enter data

CORRECTLY4. Visualise your data5. 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, 52

1. Start with long hand2. Then Calculator3. Finally use Excel

1. Long Hand1. Freq Table

Mean, xbar = 427/8

= 53.375

x f xf (x-xbar) (x-xbar)2 f(x-xbar)251 1 51 -2.38 5.64 5.6452 1 52 -1.38 1.89 1.8953 2 106 -0.38 0.14 0.2854 2 108 0.63 0.39 0.7855 2 110 1.63 2.64 5.28

x f xf (x-xbar) (x-xbar)2 f(x-xbar)251 1 51 -2.38 5.64 5.6452 1 52 -1.38 1.89 1.8953 2 106 -0.38 0.14 0.2854 2 108 0.63 0.39 0.7855 2 110 1.63 2.64 5.28

x f xf (x-xbar) (x-xbar)2 f(x-xbar)251 1 51 -2.38 5.64 5.6452 1 52 -1.38 1.89 1.8953 2 106 -0.38 0.14 0.2854 2 108 0.63 0.39 0.7855 2 110 1.63 2.64 5.28

x f xf (x-xbar) (x-xbar)2 f(x-xbar)251 1 51 -2.38 5.64 5.6452 1 52 -1.38 1.89 1.8953 2 106 -0.38 0.14 0.2854 2 108 0.63 0.39 0.7855 2 110 1.63 2.64 5.28

x f xf (x-xbar) (x-xbar)2 f(x-xbar)251 1 51 -2.38 5.64 5.6452 1 52 -1.38 1.89 1.8953 2 106 -0.38 0.14 0.2854 2 108 0.63 0.39 0.7855 2 110 1.63 2.64 5.28

427n = 8

13.875

Variance = 13.875/(8-1)=1.98

SD = Variance = 1.98 =1.41

55, 54, 51, 55, 53, 53, 54, 52

2. Calculator55, 54, 51, 55, 53, 53, 54, 52

3. Excel55, 54, 51, 55, 53, 53, 54, 52

All 3 routes led to the same answers

Long Hand

Calculator

Excel

Mean

53.38 53.38 53.38

SD 1.41 1.41 1.41