Series completion.

Overview

Series completion tests the capacity to recognize a pattern across a sequence and predict its continuation. Where matrix reasoning asks what completes a two-dimensional grid, series completion asks what comes next in a one-dimensional progression. Six items of this type appear on the Standard Test; three on the Short Assessment.

The reasoning demand overlaps substantially with matrix reasoning — both require detecting what varies, inferring the rule, and applying it correctly — but the temporal framing changes the cognitive flavor. Series items feel more like asking "what happens next?" than "what fills the gap?" Different mental motion, same underlying capacity.

Question format

Each series item presents a sequence of geometric figures in order. The task is to select, from a set of candidate figures, the one that continues the sequence.

The rules governing series items fall into recognizable families:

• Additive progression — each step adds a constant quantity (one more shape, one more side, one more degree of rotation)
• Multiplicative progression — each step scales the previous by a constant factor (size doubles, count triples)
• Cyclical patterns — the sequence cycles through a fixed set of states, returning to the first state after a complete cycle
• Alternating patterns — two independent sequences interleave (ABABAB, where A and B each have their own progression)
• Transformational progression — each step applies a fixed operation to the previous (rotate 90°, reflect, invert fill)
• Dual-rule sequences — two attributes vary according to two independent rules, both of which must be tracked to predict the next item

Series items, like matrix items, are ordered by increasing complexity on the test. Early items use single straightforward rules; later items require tracking two or more independently varying attributes.

What it measures

Series completion measures sequential pattern recognition — a component of fluid intelligence specifically tied to rule extraction across time rather than across space. The capacity is closely related to what cognitive psychologists call "relational reasoning": detecting the rule that connects adjacent elements and generalizing it.

The cognitive demands include:

• Comparing consecutive elements to isolate what changed
• Testing whether the change is the same across multiple adjacent pairs (confirming a consistent rule)
• Holding the rule in working memory long enough to extend it one more step
• Ignoring attributes that are constant across the sequence (constancy is information too — it tells you which attributes are not part of the rule)

Well-designed series items include distractors that each satisfy part of the rule. A distractor might have the correct count but the wrong color, or the correct transformation but applied backward. Partial credit is not given for partial reasoning — the answer must get everything right.

Strategy and approach

Compare adjacent pairs, not the whole sequence at once

The rule is usually easier to extract from two consecutive elements than from a holistic view of the full sequence. Work out what changed between position 1 and 2, confirm the same change from 2 to 3, and extend.

Check multiple attributes

When a sequence appears to follow an obvious rule (count increases, for instance), verify that other attributes (color, shape, position) are not also varying in parallel. If they are, both rules must be applied to find the next element.

When a pattern seems to reset, look for cyclicity

If the sequence starts repeating earlier elements, you are likely looking at a cyclical rule. Identify the cycle length — usually three or four steps — and predict based on where you are in the cycle.

Alternating patterns need separate tracking

If the sequence seems erratic, check whether every other element follows a consistent rule (ABABAB structure). Each sub-sequence may have its own simple progression that is hidden by the interleaving.

Do not assume the simplest rule is always the answer

Series items at challenging difficulty often use compound rules where a simple interpretation works for the first few elements but breaks at the later elements. Always verify your rule against every given element before extending.

Example item

Consider a sequence where shapes grow progressively: a small triangle, a medium triangle, a large triangle. Each step increases the size by one level.

The distractors on such an item typically include a large outline triangle (correct size, wrong fill), a small filled triangle (wrong size, correct fill), or a medium triangle with a dot (mixing rules from different rows). Items at the challenging end layer additional attributes — rotation, color, count — each governed by an independent rule.

Practice

The practice guide includes 40 series completion problems spanning all rule families — additive, multiplicative, cyclical, alternating, transformational, and dual-rule. Worked explanations identify the governing rule and diagnose each distractor.

Begin the test to see six series completion items scored against standard population norms.