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