Chapter 11

• maturation threat - change in behaviour that emerges spontaneously over time - people adapt to changed environments

  • improvement - comparison group
• internal validity threats in one-group pretest/posttest designs

  1. maturation threats
  2. History threats
  3. Regression threats
  4. Attrition threats
  5. testing threats
  6. instrumental threats
• history threats - 'historical' or external factors that systematically effect most members of the treatment group at the same time as the treatment itself - unclear if treatment caused the change

  • improvement - comparison group
• regression threat - statistical concept - regression to the mean.

  when group average is unusually extreme at time 1 the next time the group is measured it is likely to be less extreme - closer to average performance

  works at both extremes + only occur when a group is measured twice

  • preventing - comparison groups + careful inspection of the pattern of results
• Attrition threats - when a systematic type of participant drops out of the study before it ends

  • preventing - remove scores of participants that drop out
• testing threats - change in participant as a result of taking a test more than once

  • preventing - abandon pre-test + use alternative forms of the test for the 2 measurements + comparison group
• observer bias - when researchers expectations influence their interpretations of results - threat to internal + construct validity
• demand characteristics - when participants change their behaviour to suit what they think researchers are looking for
• avoiding demand characteristics

  • double-blind study
  • masked design
• placebo effect - when people receiving treatment improve because they believe they're receiving a valid treatment

  • improving - double blind control
• null effects - finding an iv didn't make a difference in the dv - no significant covariance between the 2
• ceiling effect - scores squeezed together at the high end
• floor effect - scores cluster at low end
• manipulation checks - separate DV included
• noise - too much unsystematic variability within each group
• measurement error - human or instrument factor that can randomly inflate or deflate a persons true score on `dv
• DV score = participants true score +/- random error of measurement
• improving measurement error:

  • use reliable precise tools
  • measure more instances
• improving individual differences

  • change design to within groups
  • more participants
• situation noise - external distractions

  improving - carefully control surroundings
• power - likelihood a study will return an accurate result when the IV has an effect
• null effects should be reported transparently