# Machine Learning

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##### What are ratio variables?
This is a subtype of interval variables where ratio of scales is used for measurement.
For Example, Water representation in chemistry is H2O which represents two molecules of hydrogen and one molecule of oxygen. Thus, the ratio of elements is 2: 1.
##### What are Univariate and Bivariate variables?
Univariate variable: When the variable under consideration is only one then it is called univariate variable study.
Bivariate variable: Involves study of relationship between two variables.
##### What is measurement error?
The discrepancy between the measured value and actual value in terms of number is called measurement error.
For Example While buying fruits from a vendor in kilograms, if we wanted 1 kilogram of fruits and the vendor’s weighing machine showed 1 kilogram when we brought the same. After checking the same in another machine, if the measured value shows 0.1 kilogram less than expected then this difference is what we call as measurement error.
##### Explain Validity?
Validity implies whether an instrument measures what it is supposed to measure.
##### Explain Reliability?
Reliability implies whether the instrument gives consistent result across different conditions.
For example, if we test the same value twice on the same entity then the results from the instrument should remain same if it has to be reliable. Such tests are known as test-retest.