_HP-71B AMPI Statistics Library_ Equipment required: HP-71B Optionally : Printer Mass Storage This article describes the AMPI Statistics 32K ROM pac. It should be thought of more as a product description with comments, than as an in depth review, as I have not had cause to use this pac in 'anger.' The pac may be used either from a menu program or specific routines may be called up from user's programs. All the facilities offered by the pac may be accessed using either method. In addition the menu program offers facilities to create data arrays, edit them, print the data, and to load and save the data in HPAF format. (Hewlett Packard Applications File format. This allows swapping of data with other programs following the standard, eg. the curve fitting rom.) The statistical facilities offered by the pac are best summarised by reproducing part of a table from the manual. Function Type Program Name General Statistical Tests Descriptive Statistics Means and Moments Histogram Multiple Linear Regression Parametric Tests t-Statistics Paired t-Test Unpaired t-Test F-Statistics One-way Analysis of Variance Two-way Analysis of Variance Chi-square Statistics Contingency Table Non-Parametric Tests Rank Statistics Mann-Whitney U Test Kruskal-Wallis Test Statistical Distributions Sampling Distributions Students Distribution F-Distribution Chi-Distribution Probability Distributions Normal Distribution Weibull Distribution Exponential Distribution Binomial Distribution Poisson Distribution Most of the titles are self explanatory execpt for the general statistical tests and distributions. The first program calculates the arithmetic, geometric and harmonic means (where possible) and the second, third and fourth moment about the (Arithmetic) mean. It is possible to select between the sample or population for the variance (moment 2). In addition the Kurtosis and a skewness coefficient are calculated. I would have liked to have got medians as I have recently had to calculate some. Finding the medians are possible, however, by using the sort on the DEFine key in the editor. Also a very minor gripe is that I object to having to square root the variance to obtain the standard deviation, rather than the program presenting this with the other results. The second program provides a way to check the fit of a histogram of the data against six distributions :- Normal Weibull Exponential Binomial Poisson Uniform The last of the general tests is multiple linear regression. As well as finding the coefficients (standardized or not), etc, it also calculates the correlation coefficients for each pair of variables, and performs an F-test to show if there is no dependance between Y and the independant X. The distribution programs, provide a substitute for a large part of the statistical tables that are normally required. _Entering Data_ The data entering facilities are accessed from the main menu ("Data Edit Menu Quit?") under two headings; Data, which is actually a sub menu ("Kbd Load Save Print?") and Edit which enters the same data editor that is eventually used by Kbd after it has set up the array. The other options in the Data sub menu are self-explanatory, with the addition that print looks for a printer and will display an error message if not found rather than trying to use the display. Load will attempt to load any HPAF file from any package, making intelligent decisions where necessary. Choosing the Kbd option lets you set up the data format (grouped or ungrouped, number of variables and total number of observations). There is then an option to "Edit the parameters". Almost all the parts of this pac contain checks like this and so I will not always point them out in the rest of the article. I like them as they did save me from disastrous mistakes on a few occasions. The variables are labeled by default X1..Xn but these may be replaced by any one to ten character name. The '71 then drops into the editor. This is quite serviceable and allows easy entering and alteration of data. My major problem was the lack of an overlay in the review package. I checked with the Journal Editor who loaned me this package, and was informed that he was not aware of an overlay for the pac. While most of the keys are easily remembered, (eg Add is O [fO is labeled ADD on the keyboard]), an overlay would have made learning to use the editor less difficult. Data items can also be entered as expressions eg (1+SQR(25))/3. As the pac redefines the S and Q keys, it is necessary to type gSgQR for SQR. This is not really a problem as letters are entered less often than the editor options that the keys are redefined to represent. The editor is also capable of sorting columns of data, auotmatically entering a line of equally spaced values and of performing a type of macro to fill a column. (eg make X3=X1-X2). The program does seem to disable the input buffer. This is inconvenient as it forces the user to watch the display, otherwise a keystorke or two may be ignored as the machine processes the last input. _The Toolbox_ The toolbox is divided into two sections; statistical and distribution programs. These are stored in two BASIC files STP and DIST. The programs are presented as SUB programs, all of which have a standard type of call syntax. The STP section require the user to pass four arrays. Two are used to pass the raw data, and input parameters, while the other two return the statistical summary and the required output. The DIST programs take only 2 arrays, one for input and the other for the results. As a bonus the AMPILEX file in the pac contains the keyword KEYWAIT$ which waits for a key to be pressed but with the CPU powered down to conserve power, much like light sleep on the '41. This is a boon to any BASIC programmer who does not already have a lex file with this keyword. Also present is MSG$ which takes an error number and returns the error message. _The Manual_ The manual is uniformly excellent. There are examples for each program. There is just enough mathematics and theory to explain the pac without turning the manual into a statistics textbook. For those users who do need more information there is a list of recommended reading, also including some Hewlett-Packard publications for people new to the '71 and IL. _Conclusion_ It is very hard to draw a suitable conclusion to the review. The pac is the official HP product, and there are no obvious competing products. In use it was quite competent though for large data samples the "Working..." prompt was up for a potentially irritating length of time. Rabin Ezra (19)