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Zandi
Calcite | Level 5

I am trying to execute exact wilcoxon p values but the system is taking time and end up canceling. I need to know how much memory is required for a successful execution. My computer has a 16GB RAM.

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Accepted Solutions
PGStats
Opal | Level 21

Get pretty good approximation of the exact p-value by adding options MC and N= or MAXTIME= to the EXACT statement.

 

MAXTIME=value

specifies the maximum clock time (in seconds) that PROC NPAR1WAY can use to compute an exact p-value. If the procedure does not complete the computation within the specified time, the computation terminates. The maximum time value must be a positive number. This option is available for Monte Carlo estimation of exact p-values as well as for direct exact p-value computation. For more information, see the section Computational Resources.

MC

requests Monte Carlo estimation of exact p-values instead of direct exact p-value computation. Monte Carlo estimation can be useful for large problems that require a considerable amount of time and memory for exact computations but for which asymptotic approximations might not be sufficient. For more information, see the section Monte Carlo Estimation.

This option is available for all EXACT statistic-options except the HL option, which produces exact Hodges-Lehmann confidence limits. The ALPHA=, N=, and SEED= options invoke the MC option.

N=n

specifies the number of samples for Monte Carlo estimation. The value of n must be a positive integer, and the default is 10,000 samples. Larger values of n produce more precise estimates of exact p-values. Because larger values of n generate more samples, the computation time increases.

The N= option invokes the MC option.

 

 

 

PG

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4 REPLIES 4
andreas_lds
Jade | Level 19

Assumption: The amount of memory required depends on the size of data.

ballardw
Super User

From the Details of Proc Npar1way under Exact Tests:

 

A formula does not exist that can predict in advance how much time and memory are needed to compute an exact p-value for a certain problem. The time and memory required depend on several factors, including which test is being performed, the total sample size, the number of rows and columns, and the specific arrangement of the observations into table cells. Generally, larger problems (in terms of total sample size, number of rows, and number of columns) tend to require more time and memory. Additionally, for a fixed total sample size, time and memory requirements tend to increase as the number of rows and columns increase, because this corresponds to an increase in the number of tables in the reference set. Also for a fixed sample size, time and memory requirements increase as the marginal row and column totals become more homogeneous. For more information, see Agresti, Mehta, and Patel (1990) and Gail and Mantel (1977).

PGStats
Opal | Level 21

Get pretty good approximation of the exact p-value by adding options MC and N= or MAXTIME= to the EXACT statement.

 

MAXTIME=value

specifies the maximum clock time (in seconds) that PROC NPAR1WAY can use to compute an exact p-value. If the procedure does not complete the computation within the specified time, the computation terminates. The maximum time value must be a positive number. This option is available for Monte Carlo estimation of exact p-values as well as for direct exact p-value computation. For more information, see the section Computational Resources.

MC

requests Monte Carlo estimation of exact p-values instead of direct exact p-value computation. Monte Carlo estimation can be useful for large problems that require a considerable amount of time and memory for exact computations but for which asymptotic approximations might not be sufficient. For more information, see the section Monte Carlo Estimation.

This option is available for all EXACT statistic-options except the HL option, which produces exact Hodges-Lehmann confidence limits. The ALPHA=, N=, and SEED= options invoke the MC option.

N=n

specifies the number of samples for Monte Carlo estimation. The value of n must be a positive integer, and the default is 10,000 samples. Larger values of n produce more precise estimates of exact p-values. Because larger values of n generate more samples, the computation time increases.

The N= option invokes the MC option.

 

 

 

PG
Sajid01
Meteorite | Level 14

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