Search results
Results from the WOW.Com Content Network
The q-value can be interpreted as the false discovery rate (FDR): the proportion of false positives among all positive results. Given a set of test statistics and their associated q-values, rejecting the null hypothesis for all tests whose q-value is less than or equal to some threshold ensures that the expected value of the false discovery rate is .
Abstract Full text PDF Archived 2015-05-01 at the Wayback Machine; Rorabacher, D. B. (1991) "Statistical Treatment for Rejection of Deviant Values: Critical Values of Dixon Q Parameter and Related Subrange Ratios at the 95 percent Confidence Level". Anal. Chem., 63 (2), 139–146. PDF (including larger tables of limit values)
In statistics, the Q-function is the tail distribution function of the standard normal distribution. [ 1 ] [ 2 ] In other words, Q ( x ) {\displaystyle Q(x)} is the probability that a normal (Gaussian) random variable will obtain a value larger than x {\displaystyle x} standard deviations.
Q factor (bicycles), the width between where a bicycle's pedals attach to the cranks; q-value (statistics), the minimum false discovery rate at which the test may be called significant; Q value (nuclear science), a difference of energies of parent and daughter nuclides; Q Score, in marketing, a way to measure the familiarity of an item
The cumulative distribution function (shown as F(x)) gives the p values as a function of the q values. The quantile function does the opposite: it gives the q values as a function of the p values. Note that the portion of F(x) in red is a horizontal line segment.
In order to obtain the distribution in terms of the "studentized" range q, we will change variable from R to s and q. Assuming the sample data is normally distributed, the standard deviation s will be χ distributed. By further integrating over s we can remove s as a parameter and obtain the re-scaled distribution in terms of q alone.
Cochran's Q test should not be confused with Cochran's C test, which is a variance outlier test. Put in simple technical terms, Cochran's Q test requires that there only be a binary response (e.g. success/failure or 1/0) and that there be more than 2 groups of the same size.
The value q s is the sample's test statistic. (The notation | x | means the absolute value of x; the magnitude of x with the sign set to +, regardless of the original sign of x.) This q s test statistic can then be compared to a q value for the chosen significance level α from a table of the studentized range distribution.