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Preparing to Analyse Data
C.AdithanDepartment of Pharmacology
JIPMERPondicherry - 605006
NominalNominal ProportionProportionCategoricalCategorical
OrdinalOrdinal Scores, RanksScores, Ranks
ContinuousContinuousNumericalNumerical IntervalInterval
DiscreteDiscrete
Types of DataTypes of DataCategories of MeasurementCategories of Measurement
Nominal scale:
e.g., Male, Female Hindu, Muslim, Christians
- Expressed in proportions (60% male, 40% female)
Ordinal scale:
e.g., Mild, Moderate, Severe pain Light, average, heavy, very heavy smokers
- Expressed as Scores and Ranks
Data can be arranged in an ORDER and RANKED
Interval/Ratio scale:
Highest order of the measurementAssume equal intervals in its measurement
Interval scale:
- Does not have an absolute zero point e.g., Temperature on the centigrade scale
Ratio scale:
- Has an absolute zero point e.g., blood sugar
For Statistics Interval and Ratio Scales are treated as SAME
Analysis of Data: Consider 4 specific aspects
Checking of Data Missing Data Outliers
- Affect Mean SEM; Regression analysis Transformations
- logarithmic- Square root- reciprocal
Outlier
r value
With outlier: 0.65Without outlier : 0.07
Summary Statistics:
Arithmetic mean Mode Median SD SEM Proportion Confidence Interval (C.I.)
Measures of Central Tendency
Arithmetic mean: Sum of all values divided by Number of observations
Mode Most common value observed
Median Value that comes half-way when the data are ranked in order
1 2 3 4 5 5 8Mean= 28/7 = 4, Mode=5, Median=4
1 2 5 3 4 5 8
Measures of DispersionRange: Difference between lowest and highest scores in a set of data
SD: describes the variability of observations about the mean
SEM: describes the variability of means
80, 70, 80, 5, 2, 3,1 Range=80-1=7980, 6, 7, 30,12, 2,1 Range=80-1=79
80, 70, 80, 5, 2, 3,1 S.D.= 34.4 ± 39.780, 6, 7, 30,12, 2,1 S.D.= 19.7 ± 28.3
80, 70, 80, 5, 2, 3,1 SEM= 34.4 ± 15.080, 6, 7, 30,12, 2,1 SEM= 19.7 ± 10.7
Measures of Dispersion
Confidence Interval
Describes the limit within which 95% of mean values, if determined in similar experiments are likely to fall
Lower limit = mean – (t 0.05 x SEM)Upper limit = mean + (t 0.05 x SEM)
80, 70, 80, 5, 2, 3,1 95 % C.I. = 34.4 (-2.2, 71.1)80, 6, 7, 30,12, 2,1 95 % C.I. = 19.7 (-6.5, 45.9)
Rounding of NumbersRounding of Numbers85.345
85.364
17.75017.850
85.348074
85.35
85.3
85.4
85.3
85.35
17.8
17.8