View
231
Download
6
Category
Preview:
Citation preview
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
Recommended