SEE_ALSO

## NAME

coxhazard -- Compute the correlation probability by Cox's proportional hazard model.

## USAGE

`coxhazard input`

## DESCRIPTION

The `coxhazard` task computes a correlation probability by Cox's
proportional hazard model. The Cox hazard model can treat several
independent variables if the dependent variable contains only one kind
of censoring (i.e., upper or lower limits).

The Cox correlation is known to be inaccurate when many tied values are present in the data. Ties are particularly common when the data are binned. Caution should be used in these cases.

Cox regression, though widely used in biostatistical applications, formally applies only if the "hazard rate" is constant; that is, the cumulative distribution function of the censored variable falls exponentially with increasing values. Astronomical luminosity functions, in contrast, are frequently modeled by power law distributions. It is not clear whether the results of a Cox regression are significantly affected by this difference.

The test assumes the null hypothesis. The probability given by this program is the probability that there is no correlation between the variables. If the probability is small, that means "the probability that these two variables are not correlated is small" or approximately "these variables are correlated". If you see the result 0.000, it means "< 0.001".

## PARAMETERS

- input [string]
- Input file(s); this can be a list of files. Following each file name
is a list of column names in brackets. Thes column names specify which
columns in the file contain the information used by this task. The
brackets MUST contain at least three names in the following format:
[censor_indicator, independent_vars, dependent_var]. If there is more
than one independent variable, the column names all follow the censor
indicator. The censor indicator specifies the censorship of the data
point. The different kinds of censorship are explained in the censor
help file. If the input file is an STSDAS table, the names in brackets
are the table column names. If the input file is a text file, the
names in brackets are the column numbers. A title string will be
printed if the input file is a table containing the header parameter
`TITLE`.

- (verbose = no) [boolean]
- Provide detailed output?
The detailed output includes the number of data points and the number of censored points and type of censorship.

## EXAMPLES

1. Apply `coxhazard` to the data in the table "kriss.tab", using the
columns "Censor" for the censoring indicator, "LogL1mu" for the first
independent variable column, "LogL2500A" for the second independent
variable column, and "LogL2keV" for the dependent variable column.
Then use the file "iraslum.dat" (text file), columns 1, 2, and 3
(censor, independent, dependent). Several files may be processed
sequentially. The following example will compute the Cox-hazard
correlation probability for the two files indicated:

st> coxhazard kriss.tab[Censor,LogL1mu,LogL2500A,LogL2keV], \ >>> iraslum.dat[c1,c2,c3]

## BUGS

## SEE ALSO

censor, survival

Type "help statistics option=sys" for a higher-level description of
the `statistics` package.