_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)