Research Summaries · Lesson 5

Which result supports or weakens a hypothesis

A hypothesis question gives you a claim and asks whether the results support it, weaken it, or say nothing about it. First restate the claim as a prediction you can check: if the claim is true, then the count should go up every time the light goes up. Then go to the study that actually varied that factor and read the rows in order.

Many of these questions have "Yes, because… / No, because…" choices. Decide the verdict first, then check the reason. The reason must cite data from the right study, read the trend in the right direction, and actually address the claim. Two choices usually share the right verdict, and only one of them has the right reason.

Watch the exact wording of the claim. Always, every, and the same amount make a claim easy to weaken, because one row that breaks the pattern is enough. A result outside the range the claim covers, or from a study that never varied the factor, neither supports nor weakens it.

Duckweed Growth

Duckweed is a tiny floating plant made of flat leaflike parts called fronds. Students started each of several containers with 20 duckweed fronds floating on 1 L of pond-water solution kept at 22 °C under the same type of lamp. After 10 days, they counted the fronds in each container.

Study 1

Every container held a solution with 5 mg/L of nitrate, a plant nutrient. The lamps were left on for a different number of hours per day in each container. The results are shown in Figure 1.

Study 2

The lamps were on for 12 hours per day in every container. The solutions held 5 different nitrate concentrations, in milligrams per liter (mg/L). The results are shown in Table 1.

Figure 1
Figure 1Study 1, every solution at 5 mg/L of nitrate. One series, 5 mg/L nitrate: the frond count after 10 days rose with hours of light per day and nearly leveled off at the top. 4 h: 31 fronds; 8 h: 52; 12 h: 78; 16 h: 96; 20 h: 97.020406080100048121620Light per day (h)Fronds after 10 days
  • 5 mg/L nitrate
Show the data as a table
Figure 1: data
Light per day (h)5 mg/L nitrate
431
852
1278
1696
2097

Study 1, every solution at 5 mg/L of nitrate. One series, 5 mg/L nitrate: the frond count after 10 days rose with hours of light per day and nearly leveled off at the top. 4 h: 31 fronds; 8 h: 52; 12 h: 78; 16 h: 96; 20 h: 97.

Table 1
Nitrate (mg/L)Fronds after 10 days
026
249
578
1081
2058
Study 2, 12 hours of light per day: the frond count after 10 days rose with nitrate up to 10 mg/L, then fell. 0 mg/L: 26 fronds; 2 mg/L: 49; 5 mg/L: 78; 10 mg/L: 81; 20 mg/L: 58.
Checking a hypothesis
Claim says…Prediction to checkA result that weakens it
More X gives more YY rises at every step as X risesAny step where Y falls as X rises
X always increases YNo row breaks the rise, including the lastOne higher X with a lower Y
Each step adds the same amountEqual differences between neighboring rowsDifferences that grow or shrink
Above some value, X lowers YY falls for X values past that pointA result past that point that is higher, not lower

Worked example Medium

Show the whole passage

Duckweed Growth

Duckweed is a tiny floating plant made of flat leaflike parts called fronds. Students started each of several containers with 20 duckweed fronds floating on 1 L of pond-water solution kept at 22 °C under the same type of lamp. After 10 days, they counted the fronds in each container.

Study 1

Every container held a solution with 5 mg/L of nitrate, a plant nutrient. The lamps were left on for a different number of hours per day in each container. The results are shown in Figure 1.

Study 2

The lamps were on for 12 hours per day in every container. The solutions held 5 different nitrate concentrations, in milligrams per liter (mg/L). The results are shown in Table 1.

Figure 1
Figure 1Study 1, every solution at 5 mg/L of nitrate. One series, 5 mg/L nitrate: the frond count after 10 days rose with hours of light per day and nearly leveled off at the top. 4 h: 31 fronds; 8 h: 52; 12 h: 78; 16 h: 96; 20 h: 97.020406080100048121620Light per day (h)Fronds after 10 days
  • 5 mg/L nitrate
Show the data as a table
Figure 1: data
Light per day (h)5 mg/L nitrate
431
852
1278
1696
2097

Study 1, every solution at 5 mg/L of nitrate. One series, 5 mg/L nitrate: the frond count after 10 days rose with hours of light per day and nearly leveled off at the top. 4 h: 31 fronds; 8 h: 52; 12 h: 78; 16 h: 96; 20 h: 97.

Table 1
Nitrate (mg/L)Fronds after 10 days
026
249
578
1081
2058
Study 2, 12 hours of light per day: the frond count after 10 days rose with nitrate up to 10 mg/L, then fell. 0 mg/L: 26 fronds; 2 mg/L: 49; 5 mg/L: 78; 10 mg/L: 81; 20 mg/L: 58.

A student hypothesized that the more hours of light duckweed receives per day, the more fronds it will have after 10 days. Do the results of Study 1 support this hypothesis?

  1. Yes, because the frond count rose from 26 to 81 as the nitrate rose from 0 mg/L to 10 mg/L.
  2. No, because the frond count fell from 81 to 58 when the nitrate rose from 10 mg/L to 20 mg/L.
  3. Yes, because the frond count rose at every step, from 31 fronds at 4 h to 97 fronds at 20 h.Answer
  4. No, because the frond count fell as the number of hours of light per day increased.

How to solve it

  1. Restate the claim as a prediction: in Study 1, which varied light, the frond count should rise every time the hours of light rise.
  2. Read Figure 1 in order: 31, 52, 78, 96, and 97 fronds at 4, 8, 12, 16, and 20 h. The count rises at every step, so the verdict is Yes.
  3. Two choices say Yes. Choice A cites nitrate data from Study 2, which held light at 12 h, so its reason is about the wrong factor. Choice C cites Study 1 and reads it correctly.

Why each choice is right or wrong

  • A. Incorrect. The verdict is right, but the reason cites nitrate data from Study 2 (Table 1), where the light was fixed at 12 h; it says nothing about hours of light.
  • B. Incorrect. The fall from 81 to 58 fronds is Study 2’s nitrate result (Table 1). Study 1, the light study, never shows a drop.
  • C. Correct. In Figure 1, the count rises at every step: 31, 52, 78, 96, and 97 fronds at 4, 8, 12, 16, and 20 h of light per day. Each increase in light gave more fronds.
  • D. Incorrect. This reverses the trend: Figure 1 rises from 31 fronds at 4 h to 97 fronds at 20 h.

Worked example Hard

Show the whole passage

Duckweed Growth

Duckweed is a tiny floating plant made of flat leaflike parts called fronds. Students started each of several containers with 20 duckweed fronds floating on 1 L of pond-water solution kept at 22 °C under the same type of lamp. After 10 days, they counted the fronds in each container.

Study 1

Every container held a solution with 5 mg/L of nitrate, a plant nutrient. The lamps were left on for a different number of hours per day in each container. The results are shown in Figure 1.

Study 2

The lamps were on for 12 hours per day in every container. The solutions held 5 different nitrate concentrations, in milligrams per liter (mg/L). The results are shown in Table 1.

Figure 1
Figure 1Study 1, every solution at 5 mg/L of nitrate. One series, 5 mg/L nitrate: the frond count after 10 days rose with hours of light per day and nearly leveled off at the top. 4 h: 31 fronds; 8 h: 52; 12 h: 78; 16 h: 96; 20 h: 97.020406080100048121620Light per day (h)Fronds after 10 days
  • 5 mg/L nitrate
Show the data as a table
Figure 1: data
Light per day (h)5 mg/L nitrate
431
852
1278
1696
2097

Study 1, every solution at 5 mg/L of nitrate. One series, 5 mg/L nitrate: the frond count after 10 days rose with hours of light per day and nearly leveled off at the top. 4 h: 31 fronds; 8 h: 52; 12 h: 78; 16 h: 96; 20 h: 97.

Table 1
Nitrate (mg/L)Fronds after 10 days
026
249
578
1081
2058
Study 2, 12 hours of light per day: the frond count after 10 days rose with nitrate up to 10 mg/L, then fell. 0 mg/L: 26 fronds; 2 mg/L: 49; 5 mg/L: 78; 10 mg/L: 81; 20 mg/L: 58.

A student hypothesized that raising the nitrate concentration of the solution always increases the number of fronds after 10 days. Do the results of Study 2 support this hypothesis?

  1. Yes, because the frond count rose from 26 at 0 mg/L of nitrate to 81 at 10 mg/L of nitrate.
  2. No, because 20 mg/L of nitrate gave 58 fronds, fewer than the 81 fronds at 10 mg/L.Answer
  3. No, because the count rose by only 1 frond from 16 h to 20 h of light.
  4. No, because the containers with 0 mg/L of nitrate had fewer fronds than those with 2 mg/L.

How to solve it

  1. Restate the claim: if nitrate always helps, every higher concentration in Table 1 should give more fronds, including the last row.
  2. Read Table 1 in order: 26, 49, 78, 81, then 58 fronds. The last step, 10 mg/L to 20 mg/L, goes down, so the verdict is No.
  3. Three choices say No. Choice C cites light data from Study 1, and choice D cites a rise, which agrees with the claim. Only choice B gives the drop that breaks always.

Why each choice is right or wrong

  • A. Incorrect. The rise from 26 to 81 fronds is real (Table 1), but it stops at 10 mg/L. At 20 mg/L the count fell to 58, so nitrate does not always help.
  • B. Correct. Table 1 rises from 26 to 81 fronds up to 10 mg/L, then falls to 58 fronds at 20 mg/L. One higher concentration with fewer fronds is enough to weaken always.
  • C. Incorrect. The verdict is right, but the reason cites light data from Study 1 (96 to 97 fronds, Figure 1); the claim is about nitrate, which Study 1 held at 5 mg/L.
  • D. Incorrect. The verdict is right, but the reason backs the claim: 26 fronds at 0 mg/L and 49 at 2 mg/L (Table 1) is a rise with more nitrate, not a reason to reject it.

Trap The right verdict with the wrong reason

In a "Yes, because… / No, because…" question, the trap choice has the verdict you reached and a reason that cites the wrong study or misreads the trend. Check three things in the reason: it names data from the study that varied the factor in the claim, its numbers match the figure, and those numbers really point the way the verdict says.