How to Troubleshoot Tables that Take a Long Time to Compute

Sometimes it may take upwards of 30 seconds for a table to render, which can be a bit disruptive when using Q. If a table is slow to calculate or seems to take a unreasonably long-time to compute, sometimes it is the nature of the table, but other times there may be things you can do to address the root cause of the slowness. Reasons why tables take a long time to compute:

The table is using a large amount of data. For example, a Pick Any - Grid question with 20 rows and 20 columns will be computed using 400 variables, and will thus take time to both extract the data and compute the variables. This is also compounded by the number of statistics shown on the table, rules applied, and if you stat testing using column comparisons (vs arrow and font colors which don't need to run as many individual tests).
You are using banners when there is no need to use them. For example:
- If there is only one question in your banner, it will generally be much faster to select that question in the Brown Drop-down Menu rather than use a Banner. The reason for this is that in the underlying computations, Q treats each category of the banner as a single variable. Thus if you have a question with, say, 100 categories, it creates 100 variables, which can substantially slow down performance.
- If a banner consists of nested Pick One questions, such as gender-within-age, creating a new JavaScript Variable will achieve substantially faster computational performance. For example, if Gender has 2 categories and Age as 10, the following Expression will create a new variable with the nesting: Age + Gender * 10.
- If a banner includes a variable that is only being used as a filter, it will generally be substantially faster to remove it from the banner, and instead, use it to Filter the table.
Excel-Style Formulas are being used with a large amount of data. Excel-style variables are much slower than JavaScript Variables. You probably won't notice the difference when you have thousands of cases, but you will if you have hundreds of thousands of cases.
The variables being used in the table are JavaScript Variables (including Linked variables) which are computed using lots of other variables. When such variables are used in analysis Q needs to first load all the input variables and then compute the variables prior to computing the table.
An Experiment or Ranking question is being analyzed. Advanced models are running in the background to calculate the coefficients and probabilities shown on the table. This can be exacerbated by the number of variables grouped in the question and cases in the variables.
The table is very large. For example, where an ID variable is set as a Pick One question then any table that uses this question will be very large (e.g., if you have 10,000 respondents in the data file the table will contain 10,000 rows or columns).
If JavaScript variables are very slow then consider using Tools | Save Data as SPSS File… to save out a copy of your data file with the calculations already done. This will make a larger data file, but may save time overall. (Before doing this Hide any variables that are not used in tables/charts so that they are excluded from the new data file.)