Confidence limits are two extremes of a measurement within which 95% observations would lie.

**Confidence
Interval (CI):**

Confidence limits are two extremes of a
measurement within which 95% observations would lie. These describe the limits
within which 95% of the mean values if determined in similar experiments are
likely to fall. The value of ‘t’ corresponding to a probability of 0.05 for the
appropriate degree of freedom is read from the table of distribution. By
multiplying this value with the standard error, the 95% confidence limits for
the mean are obtained as per formula below.

Lower
confidence limit = mean - (t0.05 × SEM) Upper confidence limit = mean + (t0.05
× SEM) If n > 30, the interval M ± 2(SEM) will include M with a probability
of 95% and the interval M ± 2.8 (SEM) will include M with probability of 99%.
These intervals are, therefore, called the 95% and 99% confidence intervals,
respectively. The important difference between the ‘p’value and confidence
interval is that confidence interval represents clinical significance, whereas
‘p’ value indicates statistical significance. Therefore, in many clinical
studies, confidence interval is preferred instead of ‘p’ value, and some
journals specifically ask for these values. Various medical journals use mean
and SEM to describe variability within the sample. The SEM is a measure of
precision for estimated population mean, whereas SD is a measure of data
variability around mean of a sample of population. Hence, SEM is not a
descriptive statistics and should not be used as such. Correct use of SEM would
be only to indicate precision of estimated mean of population.

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