(a) Approximations in measurements, e.g., the heights of individuals may be approximated to 10th of a centimeter, age may be measured correct to nearest month, weight may be measured correct to 10th of a kilogram, distance may be measured correct to the nearest metre and so on. Thus, in all such measurements, there is bound to be a difference between the observed value and the true value.
(b) Approximation in rounding of the figures to the nearest hundreds, thousands, millions, etc., or in the rounding of decimals.
(c) The biases duet of faculty collection and analysis of the data and biases in the presentation and interpretation of the results.
(d) Personal biases of the investigators and so on.