ADI decimation function

Been looking at the ADI library, specifically fir_decima

FIR-based decimation filter
Synopsis
#include <filter.h>
float *fir_decima (const floatinput[],
floatoutput[],
const float pmcoefficients[],
floatdelay[],
intnum_output_samples,
intnum_coeffs,
intdecimation_index);
Description

The fir_decima function implements a finite impulse response (FIR)
filter defined by the coefficients and the delay line that are
supplied in the call of fir_decima. The function produces the filtered
response of its input data and then decimates. The size of the output
vector output is specified by the argument num_output_samples, which
specifies the number of output samples to be input should contain
generated. The input vector input should contain
decimation_index*num_output_samples samples, where decimation_index
represents the decimation index.

What is the relationship between the number of input and output
samples and ticksize, since the numbers are different?

Dirk