Statistics formats described
This section lists the important statistics formats settings in QPSMR Companion.
Mean scores, averages & other statistics from values or scores
There are two sorts of questions that will produce various statistics when used as the rows of a table. The first type are quantities, usually Integer or Float entries. For example, salary, height or volume. For these questions when you use them as the rows of the table, either a full list of values can be requested, or the statistics only. The second type is scored questions, often rating scales to which scores (values) have been assigned. For example:
Like a lot (2) Like a little (1) Indifferent (0) Dislike a little (-1) Dislike a lot (-2)
Tables which normally show the full list of values as the rows may be displayed with or without the individual rows (format DIS). Using format NDIS means that only the requested statistics are output (no distributions).
Furthermore, Companion shows the values to use for statistics in parentheses (as above using format PSV). You can also control the decimal places for float entries by format PSD.
When using these types of entries on your tables the following statistics may be produced:
- Base for statistics (format BST)
- Sum of values (format SUM)
- Sum of squares of values (format SSQ)
- Average or mean score (format AVG)
- Standard deviation (format SDV)
- Standard error (format SER)
- Error variance (format EVR)
- Mean score divided by standard error (format MSE)
You can control the decimal places for AVG by format DPA. All other statistics are controlled by format DPS.
For tables with all rows listed (not statistics only tables), you can also request the following:
- Medians (format MED)
- Quartiles to Deciles (format ILE)
- Maximum value (format ILH)
- Minimum value (format ILL)
- Modal value (format MOD)
IMPORTANT: The calculations listed above assume that the values are in ascending order. You should always use format RNA when tabulating quantity questions which list all rows.
If you use the statistics formats TTF with SHG, Companion will perform an F-test on all the columns within each group. You can use this test to establish whether the group of columns (for example – Area) affects the row mean or average, without looking at all of the individual pairs of columns.
Statistics formats SLA, SLB and SLC control the levels to be tested. A setting of 101 means that the level is not used. The standard setting for these formats is SLA95/SLB99/SLC101/SLD101.
If you only use lower case letters as identifiers, upper case means SLB level. SLC adds an additional + (plus) to the front of each marker. For total comparisons this may be an additional – (minus).
Distribution Z test & t-test markers
If your table has a list of independent rows, you can use format SIG to mark significant differences. There must be a total row for the Z test or t-test calculations to work.
Each row of the table is treated separately and cells are marked depending on whether the prportion is different to the other columns in the same row in the column it is being compared with.
You can also choose Z test to use the combined variance (pooled) with SIG1, or separate variances (un-pooled) with SIG2. In addition, you can choose t test without continuity correction SIG3 (default), or with continuity correction SIG4.
For overlapping t tests the formats are SIG5 and SIG6. This will not affect the tests against total for which SIG3 and SIG4 will still be used.
Mean or average t test markers
Where a table has rows from which a mean score or average is produced, significant differences will be marked. If you do not wish to include these markers, you should set format option TTV0. You may choose whether to use the combined variance with TTV1 or separate variances with TTV2.
If a respondent rates two or more products, you could produce a banked table with the products as the breakdown and use column identifiers to compare them. Significantly, a more accurate method which is not often used is to subtract the score for one product from the score for the other. For example, with scores 1 to 5 the relative score will be between –4 and +4. This relative score can then be tabulated and format MSE will give a t test value comparing the mean score with the expected fixed value of 0.0. When the expected value for a mean is zero, if format MSE is >1.96, this is 95% significant and >2.57 is 99%.
Data from Companion can be output to other specialised software for further statistical tests.