This example demonstrates how procedures save statistical analysis context and results into item stores and how you can use
PROC PLM to make post hoc inference based on saved item stores. The data are taken from McCullagh and Nelder (1989) and concern the effects on taste of various cheese additives. Four cheese additives were tested, and 52 response ratings
for each additive were obtained. The response was measured on a scale of nine categories that range from strong dislike (1)
to excellent taste (9). The following program saves the data in the data set `Cheese`

. The variable `y`

contains the taste rating, the variable `Additive`

contains cheese additive types, and the variable `freq`

contains the frequencies with which each additive received each rating.

data Cheese; do Additive = 1 to 4; do y = 1 to 9; input freq @@; output; end; end; label y='Taste Rating'; datalines; 0 0 1 7 8 8 19 8 1 6 9 12 11 7 6 1 0 0 1 1 6 8 23 7 5 1 0 0 0 0 1 3 7 14 16 11 ;

The response `y`

is a categorical variable that contains nine ordered levels. You can use PROC LOGISTIC to fit an ordinal model to investigate
the effects of the cheese additive types on taste ratings. Suppose you also want to save the ordinal model into an item store
so that you can make statistical inference later. You can use the following statements to perform the tasks:

proc logistic data=cheese; freq freq; class additive y / param=glm; model y=additive; store sasuser.cheese; title 'Ordinal Model on Cheese Additives'; run;

By default, PROC LOGISTIC uses the cumulative logit model for the ordered categorical response. The STORE statement saves
the fitted model to a SAS item store named `sasuser.cheese`

. The name is a two-level SAS name of the form `libname.membername`

. If `libname`

is not specified in the STORE statement, the fitted results are saved in `work.membername`

and the item store is deleted after the current SAS session ends. With this example, the fitted model is saved to an item
store named `sasuser.cheese`

in the Sasuser library. It is not deleted after the current SAS session ends. You can use PROC PLM to restore the results
later.

The following statements use PROC PLM to load the saved model context and results by specifying RESTORE= with the target item
store `sasuser.cheese`

. Then they use two SHOW statements to display separate information saved in the item store. The first SHOW statement with
the PROGRAM option displays the program that was used to generate the item store `sasuser.cheese`

. The second SHOW statement with the PARMS option displays parameter estimates and associated statistics of the fitted ordinal
model.

proc plm restore=sasuser.cheese; show program; show parms; run;

Output 73.2.1 displays the program that generated the item store `sasuser.cheese`

. Except for the title information, it matches the original program.

Output 73.2.1: Program Information from `sasuser.cheese`

Ordinal Model on Cheese Additives |

The PLM Procedure

SAS Program Information |
---|

proc logistic data=cheese; |

freq freq; |

class additive y / param=glm; |

model y=additive; |

store sasuser.cheese; |

run; |

Output 73.2.2 displays estimates of the intercept terms and covariates and associated statistics. The intercept terms correspond to eight cumulative logits defined on taste ratings; that is, the ith intercept for ith logit is

Output 73.2.2: Parameter Estimates of the Ordinal Model

Parameter Estimates | |||
---|---|---|---|

Parameter | Taste Rating |
Estimate | Standard Error |

Intercept | 1 | -7.0801 | 0.5624 |

Intercept | 2 | -6.0249 | 0.4755 |

Intercept | 3 | -4.9254 | 0.4272 |

Intercept | 4 | -3.8568 | 0.3902 |

Intercept | 5 | -2.5205 | 0.3431 |

Intercept | 6 | -1.5685 | 0.3086 |

Intercept | 7 | -0.06688 | 0.2658 |

Intercept | 8 | 1.4930 | 0.3310 |

Additive 1 | 1.6128 | 0.3778 | |

Additive 2 | 4.9645 | 0.4741 | |

Additive 3 | 3.3227 | 0.4251 | |

Additive 4 | 0 | . |

You can perform various statistical inference tasks from a saved item store, as long as the task is applicable under the model context. For example, you can perform group comparisons between different cheese additive types. See the next example for details.