sampsize               package:epicalc               R Documentation

_S_a_m_p_l_e _s_i_z_e _c_a_l_c_u_l_a_t_i_o_n

_D_e_s_c_r_i_p_t_i_o_n:

     Sample size calculation for epidemiological studies

_U_s_a_g_e:

     n.for.survey(p, delta = 0.5 * min(c(p, 1 - p)), popsize = FALSE, 
         deff = 1, alpha = 0.05) 
     n.for.2means (mu1, mu2, sd1, sd2, ratio = 1, alpha = 0.05, power = 0.8) 
     n.for.2p (p1, p2, alpha = 0.05, power = 0.8, ratio = 1) 
     n.for.lqas (p0, q = 0, N = 10000, alpha = 0.05, exact = FALSE) 

_A_r_g_u_m_e_n_t_s:

       p: estimated prevalence

   delta: difference between the estimated prevalence and one side of
          the 95 percent confidence limit

 popsize: size of the finite population

    deff: design effect for cluster sampling

   alpha: significance level

mu1, mu2: estimated means of the two populations

sd1, sd2: estimated standard deviations of the two populations

   ratio: n2/n1

  p1, p2: estimated probabilities of the two populations

   power: power of the study

      p0: critical proportion beyond which the lot will be rejected

       q: critical number of faulty pieces found in the sample, beyond
          which the lot will be rejected

       N: lot size

   exact: whether the exact probability is to be computed

_D_e_t_a_i_l_s:

     'n.for.survey' is used to compute the sample size required to
     conduct a survey.  When cluster sampling is employed, the design
     effect (deff) has to be taken into account.

     'n.for.2means' is used to compute the sample size for testing a
     hypothesis of difference of two population means.

     'n.for.2p'  is used to the compute the sample size for testing a
     hypothesis of difference of two population proportions.

     For a case control study, p1 and p2 are the proportions of
     exposure among cases and controls.

     For a cohort study, p1 and p2 are proportions of positive outcome
     among the exposed and non-exposed groups.

     'ratio' in a case control study is controls:case. In cohort and
     cross-sectional studies, it is non-exposed:exposed.

     LQAS stands for Lot Quality Assurance Sampling. The sample size n
     is determined to test whether the lot of a product has a defective
     proportion exceeding a critical proportion, p0. Out of the sample
     tested, if the number of defective specimens is greater than q,
     the lot is considered not acceptable. This concept can be applied
     to quality assurance  processes in health care.

_A_u_t_h_o_r(_s):

     Virasakdi Chongsuvivatwong <cvirasak@medicine.psu.ac.th>

_S_e_e _A_l_s_o:

     'power.for.2means', 'power.for.2p'

_E_x_a_m_p_l_e_s:

     # In a standard survey to determine the coverage of immunization using 
     # a cluster sampling technique on the population of approximately 500000,
     # the estimated prevalence is 70 percent, design effect is assumed to be 2.

     n.for.survey( p = .8, delta = .1, popsize = 500000, deff =2) # 123

     # In a case control study testing the efficacy of measles vaccine. 
     # The coverage in the non-diseased population is estimated at 80 percent. 
     # That in the diseased is 60 percent.

     n.for.2p(p1=.8, p2=.6) # n1=n2=91

     # A randomized controlled trial testing cure rate of a disease of
     # 90 percent by new drugs  and 80 percent by the old one.

     n.for.2p(p1=.9, p2=.8) # 219 subjects in each arm.

     # A quality assurance to check whether the coding of ICD-10 is faulty 
     # by no more than 2 percent.The minimum sample is required. 
     # Thus any faulty coding in the sample is not acceptable.

     n.for.lqas(p0 = .02, q=0, exact=TRUE) # 148 non-faulty checks is required 
     # to support the assurance process.
      

