Download Review-1

Review-1
SPSS Training
Naveen Shrestha
Epidemiologic Study Designs
A. Descriptive studies
1. Populations (ecological studies)
2. Individuals
a. Case reports and case series
b. Cross-sectional surveys
B.
Analytic studies
1.
Observational studies
a. Case-control studies
(always retrospective)
b.
Cohort studies
(retrospective or prospective)
2.
Intervention studies
a. randomized controlled trials
b. field trials
c. community trials
Relative Risk
Results of a cohort study that followed 100 nondiabetic nurses for 15 years. At the end of the 15
years their smoking behavior was related to their
diabetic status.
Diabetic
Not Diabetic
Total
50
25
75
Smoking
20
5
25
Not smoking
70
30
100
Total
50/75
RR =
= 0.666667/0.8 = 0.833375
20/25
we can calculate the Odds Ratio for all the
suspected risk factors:
Lunch 22/1
Lunch 23/1
Salad
Sandwich
Chicken
Gastroenteritis
Eaten
Not
6
31
18
19
12
24
16
21
4
33
No Gastroenteritis
Eaten
Not
9
48
14
43
5
52
14
44
4
54
Odds Ratio
6/31 / 9/48 = 1.0
18/19 / 14/43= 2.9
12/24 / 5/52 = 5.2
16/21 / 14/44= 2.4
4/33 / 4/54 = 1.6
If the disease is rare <10% the RR and OR would be similar
P value and confidence interval
• P value reflects both the magnitude of
association and sample size
• Confidence interval (CI) is more
informative
– Wide CI = variability
Sample size
n = z2pq/l2
n = the desired sample size
z = the standard normal deviate, usually set at 1.96 (or more
simply 2.0), which corresponds to the 95 percent confidence
level.
p = the proportion in the target population estimated to have a
particular characteristics. If there is no reasonable estimate, then
use 50%
q = 1-p
l = degree of accuracy desired (0.05)
n = (2)2 (0.5) (0.5)/ (0.05)2 = 400
What is SPSS
Like a spreadsheet: stores and manipulates
numbers. Does calculations.
Like a database: Stores records about
individuals.
It is: a statistics package: others include
Statistica, Systat, BMDP, SAS.
Introduction to SPSS
SPSS is a software package used for conducting
statistical analyses, manipulating data, and generating
tables and graphs that summarize data. Statistical
analyses range from basic descriptive statistics, such
as averages and frequencies, to advanced inferential
statistics, such as regression models, analysis of
variance, and factor analysis. SPSS also contains
several tools for manipulating data, including functions
for recoding data and computing new variables as well
as merging and aggregating datasets. SPSS also has
a number of ways to summarize and display data in the
form of tables and graphs.
Data editor
Output viewer
Syntax editor