chapter 1 introduction to statistics
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CHAPTER 1 Introduction to statistics. What is Statistics?. •Statistics is the term for a collection of mathematical methods of organizing, summarizing , analyzing, and interpreting information gathered in a study . - PowerPoint PPT PresentationTRANSCRIPT
CHAPTER 1
Introduction to statistics
What is Statistics?
•Statistics is the term for a collection of mathematical methods of organizing, summarizing, analyzing, and interpreting
information gathered in a study
Data and Data AnalysisWe have two types of research study
•In quantitative research, data are usually quantitative (numbers) and subjected to
statistical analysis. Mainly the data is collected by close ended questions
•Qualitative research, data are usually narrative and collected by open ended
questions
Example of close ended question (Likert scale) to measure attitude toward mental illness
SA = Strongly agree
A = Agree
D = Disagree
SD = Strongly disagree
= ?? Uncertain
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Strongly disagree
(1)
Disagree
(2)
Uncertain(diversity)
(3)
Agree
(4)
Strongly agree
(5)
ItemsReflect the topic of the study
People who have had Mental illness can become normal and productive citizens after treatment.
Mental ill patient’s who have been in Psychiatric hospital or center should not be
allowed to have children.
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Example of open ended question• What is the perception of you organization
towered female holding high managerial positions? ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
Where Do Data Come From?•Example 1: Interviews/questionnaires
– Question: On a scale from 0 to 10, please rate your level of fatigue
– Answer (Data): Person 1: 7 Person 2: 3 Person 3: 10 Etc.
Variables
A variable is something that takes on different values
Example of variables –Height, sex, weight, age, level of education, marital status, respiratory
rate, heart rate and etc…
Types of Variables
– Independent variable: The hypothesized cause of, or influence on an outcome
– Dependent variable: The outcome of interest, hypothesized to depend on, or be caused by
the independent variable
Research Questions
•Research questions communicate the research variables and the population(the entire group of interest)
– Example: In hospitalized children (population) does music (IV) reduce stress (DV) ?
Types of Sampling
1. probability Sampling
2. Non- probability Sampling.
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Probability sample
The probability sample means, the probability
of each subject to be included in the study.
There are four types of probability sample
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Four basic kinds of probability samples. a. Simple random sample. The simple random sample is the simplest probability sample, so that every element in the population has an equal probability of being included.
Note
All types of random samples tend to be representative.
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b. Stratified random samples
In a stratified random sample, the population is first divided
into two or more homogenous strata (age, gender, occupation,
level of education, income and so forth) from which random samples are then drawn. This stratification results in greater
representativeness.
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C. Cluster samples
For many populations, it is simply impossible
to obtain a listing of all the elements, so the
most common procedure for a large surveys
is cluster sampling.
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D. Systematic samplesSystematic sampling involves the selection of every (kth) element
from some list or group, such as every 10th subject on a patient
list. If the researcher has a list, or sampling frame, the following
procedure can be adopted. The desired sample size is started
at some number (n). The size of the population must be known or
estimated (N). By dividing (N) by (n), the sampling interval is the
standard distance between the elements chosen for the sample. Dr. Yousef Aljeesh
Example if we were seeking a sample of 200 from a population of 40,000,
then our sampling interval would be as follows: K= 40,000 = 200 200In other words, every 200 the element on the list would be sampled.
The first element should be selected randomly, using a table of
random numbers, let us say that we randomly selected number
73 from a table. The people corresponding to numbers 73, 273, 473, 673, and so forth would be included in the sample.
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2. Non-probability Sample Non-probability sample is less likely than probability
sampling to produce a representative samples. Despite
this fact, most research samples in most disciplines
including nursing are non-probability samples.
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a. convenience sampling (Accidental, volunteer)
The use of the most conveniently available people or subjects in a study. For
example, stopping people at a street corner to conduct an interview is
sampling by convenience. Sometimes a researcher seeking individuals with
certain characteristics will stand in the clinic, hospital or community center to
select his convenience sample. Sometimes a researcher seeking individuals
with certain characteristics will place an advertisement in a newspaper, so the
people or subjects are volunteer to take apart of the study. Dr. Yousef Aljeesh
b. Snowball or network sampling Early sample members are asked to identify and refer other
people who meet the eligibility criteria. or it begins with a few
eligible subjects and then continues on the basic of subjects
referral until the desired sample size has been obtained. This
method of sampling is most likely to be used when the researcher
population consists of people with specific traits who might
otherwise be difficult to identify. Dr. Yousef Aljeesh
C. Quota Sampling Quota sampling is another form of non-probability sampling.
The quota sample is one in which the researcher identifies
strata of the population and determines the proportions of element needed from the various segments of the population,
but without using a random selection of subjects.
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Note: Although there are no simple formulas that indicate how large
sample is needed in a given study, we can offer a simple piece of
advice: you generally should use the largest sample possible.
The larger the sample the more representative of the population it
is likely to be.
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Variable and constant
Variable: is something that varies or takes in different values (weight, sex, blood pressure, and heart rate) are all examples of characteristics that vary from one person to the next. If they did not vary, they would be constants
Discrete Versus Continuous Variables
•Variables have different qualities with regard to measurement potential
–Discrete variables –Continuous variables
Note:- We use non-parametric tests in case of Nominal and Ordinal measurement (Example: Chi-Square test) - Both depend on percentages because Mean
does not make sense
Note In interval scale, there is no real or rational
zero point
Another Example Weight (Zero weight is actual possibility) It is acceptable to say that some one who
weights 100 kg is twice as heavy as some one who weights 50 kg.
NoteInterval and Ratio measurements are continuous
variables and parametric tests should be used in
this situation. Also Mean is applicable
Types of Statistical Analysis •Calculation
– Manual versus computerized
•Purpose– Descriptive versus inferential
•Complexity– Univariate, bivariate, multivariate
Descriptive Statistics•Researchers collect their data from a sample of
study participants—a subset of the population of interest
•Descriptive statistics describe and summarize data about the sample
– Examples: Percent female in the sample, level of education, Income, residency and ect
Example 1 of Descriptive statisticsDistribution of study population according to place of work
Hospital nameTarget
populationRespondents Percentage Response rate
Al-shifa hospital 56 51 35.7 91.07%
Nasser medical complex 21 21 14.7 100%
European Gaza hospital 21 17 11.9 80.95%
Aqsa Martyrs Hospital 14 14 9.8 100%
Kamal Adwan hospital 9 9 6.3 100%
Abu Yousef Al Najjar 12 8 5.6 66.6%
Beit Hanoun hospital 10 10 7.0 90.9%Ophthalmic hospital 7 6 4.2 85.7%Crescent Alemaraty 9 7 4.9 77.7%
Total 159 143 100.0
Calculation of Response Rate
Response Rate (RR) = Respondents (R) 100 Target Population (TP)
RR= 51 100 = 91.07 56
Example 2 of Descriptive statistics Distribution of Study Population According to Height, Weight and BMI (N= 143)
Variables Category Frequency Percentage (%)
Height (cm)
166cm and less than 41 28.7
167 – 176 cm 56 39.2
177 – 186 cm 40 28.0
187cm and above 6 4.2
Weight (kg)
Total 143 100.0
67kg and less than 32 22.4
68-78 kg 39 27.3
79-89 kg 41 28.7
90 kg and above 31 21.7
Total 143 100.0
Body Mass Index
(BMI)
Less than 25 55 0.7
22.5-29.5 33 37.8
30 and more 25 44.1
Total 143 100.0
Age distribution
25.7
45.9
28.4
05
101520253035404550
30 Yrs and less From 31 to 45 Yrs More than 45 Yrs
شرق
Example 3 of Descriptive statistics
Example 4 of Descriptive statistics Gender distribution
Example 5 of Descriptive statistics Distribution of subjects by
governorates % No. Items
13.33 15 North
11.6 13 Khanyounis
50 56 Gaza
11.6 13 Rafah
13.33 15 Mid Zone
100 112 Total
Inferential Statistics •Researchers obtain data from a sample but
often want to draw conclusions about a population
• Inferential statistics are often used to test hypotheses(predictions) about relationships between variables
Example:- Positive, negative, directional hypothesis and etc.
Example of inferential statistics
Association between socio-demographic factors and diarrhea among children aged less than 5 years (N=140)
FactorDiarrhea
χ2 p valueCasesN (%)
ControlN (%)
Father age
(20 – 30) years 33 (47.1) 37 (52.9)
7.371 0.025*(31 – 40) years 34 (48.6) 22 (31.4)
(41 – 59) years 3 (4.3) 11 (15.7)
OVC status
Orphaned 1 (1.4) 2 (2.9)
0.476 0.788Vulnerable 4 (5.7) 3 (4.3)
Not OVC 65 (92.9) 65 (92.9)
Type of familyNuclear family 46 (65.7) 50 (71.4)
0.530 0.466Extended family 24 (34.3) 20 (28.6)
Hypotheses
Definition of hypothesis : It is a statement of
predicted relationship between two or more than
two variables.
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Types of Hypotheses
1. Simple Hypothesis : A hypothesis that predicts the relationship between one dependent variable (DV) and one independent variable (IDV). It is easy to test and analyze it.
Example There is a relationship between smoking and development
of stroke among hypertensive patients in Gaza strip.
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2. Complex hypothesis: (Multivariate hypothesis) : A hypothesis that predicts the relationship between two or
more dependent variables and two or more independent variables.
Example: There is a relationship between high fat diet and smoking
and development of atherosclerosis and stroke among hypertensive patients in Gaza strip.
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3. Directional hypothesis: is one that specifies the expected direction of the relationship between variables. The researcher predicts not only the existence of a relationship but also the nature of the relationship.
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Example
1. There is a positive relationship between Smoking and lung cancer
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4. Statistical hypothesis (Null hypothesis): is one that stated there is no relationship between variables.
Example 1. There is no relationship between Smoking and lung cancer
2. There is no relationship between obesity and Breast cancer.
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