poisson.test              package:stats              R Documentation

_E_x_a_c_t _P_o_i_s_s_o_n _t_e_s_t_s

_D_e_s_c_r_i_p_t_i_o_n:

     Performs an exact test of a simple null hypothesis about the rate
     parameter in Poisson distribution, or for the ratio between two
     rate parameters.

_U_s_a_g_e:

     poisson.test(x, T = 1, r = 1,
         alternative = c("two.sided", "less", "greater"),
         conf.level = 0.95)

_A_r_g_u_m_e_n_t_s:

       x: number of events. A vector of length one or two.

       T: time base for event count. A vector of length one or two. 

       r: hypothesized rate or rate ratio

alternative: indicates the alternative hypothesis and must be one of
          '"two.sided"', '"greater"' or '"less"'. You can specify just
          the initial letter.

conf.level: confidence level for the returned confidence interval.

_D_e_t_a_i_l_s:

     Confidence intervals are computed similarly to those of
     'binom.test' in the one-sample case, and using 'binom.test' in the
     two sample case.

_V_a_l_u_e:

     A list with class '"htest"' containing the following components: 

statistic: the number of events (in the first sample if there are two.)

parameter: the corresponding expected count

 p.value: the p-value of the test.

conf.int: a confidence interval for the rate or rate ratio.

estimate: the estimated rate or rate ratio.

null.value: the rate or rate ratio under the null, 'r'.

alternative: a character string describing the alternative hypothesis.

  method: the character string '"Exact Poisson test"' or '"Comparison
          of Poisson rates"' as appropriate.

data.name: a character string giving the names of the data.

_N_o_t_e:

     The rate parameter in Poisson data is often given based on a "time
     on test" or similar quantity (person-years, population size, or
     expected number of cases from mortality tables). This is the role
     of the 'T' argument.

     The one-sample case is effectively the binomial test with a very
     large 'n'. The two sample case is converted to a binomial test by
     conditioning on the total event count, and the rate ratio is
     directly related to the odds in that binomial distribution.

_S_e_e _A_l_s_o:

     'binom.test'

_E_x_a_m_p_l_e_s:

     ### These are paraphrased from data sets in the ISwR package

     ## SMR, Welsh Nickel workers
     poisson.test(137, 24.19893)

     ## eba1977, compare Fredericia to other three cities for ages 55-59
     poisson.test(c(11,6+8+7),c(800, 1083+1050+878))

